Updated: January 19, 2002

BIOLOGY 447L

TABLE OF CONTENTS

TOPIC PAGE

SUMMARY OF COURSE EXPECTATIONS............................................................................1

INTRODUCTION .................................................................................................................... 2

1) HEART ................................................................................................................................. 5

2) ELBOW ................................................................................................................................ 15

3) KNEE .....................................................................................................................................19

4) ANKLE and FOOT ............................................................................................................... 23

5) BLOOD VESSELS OF THE HEAD, NECK & ARM ........................................................... 25

6) MUSCLES OF THE HEAD, NECK & BACK .......................................................................29

7) BLOOD VESSELS OF THE LEG.......................................................................................... 35

8) MUSCLES OF THE ARM, ABDOMEN, CHEST & PELVIS .............................................. 39

9) RESPIRATORY SYSTEM .................................................................................................... 43

10) MUSCLES OF THE LEG .................................................................................................... 45

11) SPINAL CORD ................................................................................................................... 51

12) GASTROINTESTINAL SYSTEM ...................................................................................... 53

13) PERIPHERAL NERVES ..................................................................................................... 55

14) BLOOD VESSELS OF THE ABDOMEN & URINARY TRACT ...................................... 57

15) HUMAN BRAIN ................................................................................................................ 60

16) ENDOCRINE GLANDS .................................................................................................... 69

17) CRANIAL NERVES............................................................................................................ 71

18) MALE REPRODUCTIVE TRACT ...................................................................................... 73

19) FEMALE REPRODUCTIVE TRACT ................................................................................. 77

20) EYE ..................................................................................................................................... 79

21) EAR...................................................................................................................................... 81

BRIEF SUMMARY of

COURSE EXPECTATIONS

1) You are expected to perform a fair share of the work. This will average about nine hours per week over the length of the semester. During weeks when your team is very busy, you may spend much more than nine hours, while later, when dissections are winding down, much less time may be needed. Organizing your time can be a challenge, but the course provides great flexibility in scheduling.

2) You will be expected to manage and direct at least two dissections. Team members will assist you in this assignment, but the responsibility for its completion rests solely on your shoulders. Upon its completion (no less than one week before the anatomy class is expected to study that section), you will also be expected to give an oral review to your fellow prosectors on the results of the dissection. In addition, your presentation should include information of an applied or clinical nature relating to the anatomy. Since you will inevitably spend many hours on these labs, it is suggested that you choose projects that most interest you. However, even if you're not responsible for the presentation, you are expected to know the anatomy. Lab practicals will cover all anatomical structures.

3) You are responsible for cleaning the lab during the weeks your team is at work. Needless to say, everyone is expected to pick up after themselves and to PROPERLY WRAP, SPRAY AND COVER THE CADAVERS.

4) A written summary of the dissection is to be turned in along with your presentation. This summary should state succinctly what you did, observations made, and problems encountered, along with information from your clinical applications, along with information from your clinical application. Updates and rewrites of the manual, including illustrations, should be included.

5) Grading Policies: Grades will be based about half on the two dissection/presentations and half on the two lab practical exams, a mid-term and a final. The dissection will be graded on punctuality, completeness, accuracy and overall quality. The presentation will be graded on completeness, accuracy and knowledge. In addition, there will be a grade component for "teamwork." Presenters should anticipate answering questions that might arise. Information of an applied or clinical nature can also enhance presentations. Summaries must be turned in up to a week following presentations. A written evaluation and a letter grade will be given subsequent to each presentation.

Lab practicals will be based on cadaver structures, will be identification only, and will consist of approximately 50 questions.

INTRODUCTION

First-time dissectors are often apprehensive about what appears to be a monumental and frightening task. It is important to realize that once the first incisions are made, tissue degeneration and destruction will occur. Muscle, fascia, blood vessels, bone, etc., must be cut in order to expose and label the assignments. Just remember to work slowly and carefully using the proper instruments. (Scalpels are necessary tools but should be used cautiously, especially when working in highly vascularized areas. Making deep incisions should be avoided or, when necessary, done with extreme care as many blood vessels and other structures are superficial.)

Drying will occur on the cadavers but can be reduced by spraying frequently with the wetting solution provided while working on the cadavers and by using proper wrapping procedures once work is completed for the day. Keep all regions of the body covered that aren't being worked on.

Mistakes are inevitable (we've all made them), but if the above information is followed, fewer errors will be made and many can be corrected with thread and a needle. This class is an exciting, learning experience, so ENJOY!

Some suggestions before starting:

Keep in mind the purposes of this course. They are, in order of priority:

1) Anatomical study by Bio. 247/248 students. Direct your efforts toward exposing and correctly labeling those structures needed by the A&P labs.

2) Increasing your knowledge. Take the time to carefully study anatomical structures and improve your technique.

3) Enjoyment. As long as it doesn't compromise Nos. 1 and 2, we can explore new techniques and dissections in order to make the course more rewarding.

Be patient when cutting or clearing tissue. Some vessels are very superficial and have been accidentally removed in the past by hasty prosectors. Also, realize that the tissue you're clearing away may be needed for subsequent labs. Read ahead!

Standardize your labeling techniques early. Red is good for arteries, blue for veins, yellow for nerves and green for muscles. Also, keep the length of the label string to a minimum; long labels in a tight area tend to get tangled together.

Keep the cadavers moist and covered. They have to last all year. Minutes of drying can destroy hours of work.

Remember these individuals are someone's loved ones and should be treated with respect.

REFERENCES:

1) Atlas of Human Anatomy, Frank H. Netter, M.D. Published by Ciba-Geigy Corp.

2) Color Atlas of Anatomy, Rohen/Yokochi. Published by IGAKU-SHOIN.

A NOTE ABOUT THE CLASS:

Prosection is unlike most other classes in that instruction, per se, is left to a minimum. Most of your "class time" will be spent in seminar-style presentations. Instruction will occur as teams meet with the instructor to plan upcoming dissections and to discuss procedures, anticipated problems, etc. We try to achieve that elusive "happy medium" in which each prosector has the information needed to proceed, while not being over-supervised. There are usually several equally "correct" ways of doing things. You are expected to make some mistakes, and to "learn by doing," but it is essential that IF YOU NEED MORE HELP OR MORE INFORMATION, YOU ASK FOR IT! You should also learn to avail yourself of the atlases. These will be definitive for 90% of the questions that arise. Prosection is considered by most who have taken it to be one of their favorite classes. I think this is because it provides a combination of freedom, independence and responsibility. This class gives you the opportunity to learn and excel while demonstrating your abilities, and that can lead to fulfillment, self-satisfaction and self-confidence.

A NOTE ABOUT CHEMICALS:

You will be exposed to several toxins in the course of your work. Common sense and standard safety procedures will minimize the danger.

1) The preservative in which cadavers are processed contains:

Formalin: this gas dissolved in water produces formaldehyde, a severe irritant to mucous membranes and a suspected carcinogen. Because it is a gas, formalin is very permeable to eyes and lungs.

Phenol: this substance is very caustic and also irritates mucous membranes. It can cause burns, both internally and externally.

2) The wetting solution contains phenoxyethanol, a low-toxicity and low-volatility preservative. It is also an irritant to mucous membranes.

Minimize your exposure to these substances. In general, you should take a 15-minute break for each two hours of work. If your eyes become irritated, back off and improve air circulation. If you wear contact lenses, you may need to remove them. Take note of the EYE WASH STATION in case of exposure. Always wear gloves and long sleeves to avoid skin exposure. Be careful and courteous when spraying cadavers--cover the nozzle and direct the spray away from others.

WHAT WE PROVIDE:

You will be provided wit dissection tools, which will include scissors, forceps, hemostat, scalpel handles, blunt probes, dissecting needles, bone saw, bone ronguers and various other instruments that you will need at times. We have an assortment of needles and thread for labeling. But any improvement you bring in are welcome. You will be provided with a drawer in which you may keep items you do not wish to carry back and forth to the lab.

WHAT YOU MUST PROVIDE:

You will need a lab coat (available at the Medical Bookstore and at uniform shops), gloves (available at the Medical Bookstore and at most drug stores), and scalpel blades. We have scalpel handles sized #3 and #4. These will accommodate blades #10 and #11 (fit handle #3) and #21 (fits handle #4). If your hand is small, you will want to stick to the smaller scalpel. The #10 blade (and its #21 larger counterpart) is the most useful for general cutting. The #11 blade is used for stripping of arteries, veins, nerves, etc. Other specialized blades are generally unnecessary.

TECHNIQUES AND PROCEDURES:

Blunt Dissection: This is by far the most used technique. Use a blunt probe or other object to push tissue around. This allows you te separate loose connective tissue and fat from the organs, vessels and such that you want to preserve. For a bit more force and cutting action, use the dull (reverse) edge of your scalpel.

Sharp Dissection: Use the sharp scalpel edge. This is used for initial cuts through the skin and other locations where you are sure of what and where you want to cut. If this is not the case, use blunt dissection. When cutting through skin, make a shallow cut at first, using the thumb and forefinger of the other hand to spread the skin away from the cut and to see how deep the tissue is. Once an edge or corner of the skin is free, begin separating it from the underlying tissue with blunt dissection. Examples of sharp dissection use: outer cuts through skin; severing a muscle to reflect it; severing the hemispheres of the brain; precise cuts through thin bone.

Scissor Cuts: Use scissors to cut through thin sheets such as dura mater of the brain, sclera of the eye, mesenteries, etc. Also, scissors are often safer and as useful as a scalpel for many precise cuts.

Chisels: Use these small, straight-edged blades with a small hammer for piercing through thicker bone when a scalpel can not easily be used. Examples: the last cut through the skull before brain removal; chipping through the middle ear; cutting into the eye cavity; separating the spines from the laminae of the vertebrae.

Bone Ronguers (a.k.a.: clippers, bone forceps): Use for rough cuts through ribs, clavicle, etc. Not a precise tool.

Electric Bone Saw: Used for cutting through the skull, ribs or vertebrae. This tool is temptingly easy and care must be taken to avoid cutting into tissue beneath the bone.

Fat Removal: Use mostly blunt dissection, such as the dull scalpel edge, or use forceps (tweezers) to pick away fat from muscle or other tissue. Take care so as not to damage underlying blood vessels. Fat and other tissues are disposed of in the bucket under the hood.

HEART DISSECTION

Before beginning, review the dissection of blood vessels of the head, neck and arm, and female reproduction (pp. 23 and 73).

SKIN INCISION:

1. VERTICAL: Beginning at the suprasternal notch, cut down to the level just below the xiphoid process.

2. HORIZONTAL:

A. A superior incision should be made following the clavicle laterally from the manubrium to the distal region of the acromion.

NOTE: The external jugulars are very superficial so keep the incision superficial.

B. An inferior incision from the xiphoid should follow the rib cage to the mid-axilla region, taking care not to penetrate the diaphragm. (See Figure 1.1.)

SUGGESTION: Use a marker pen to first indicate where cuts are to be made.

3. Reflect the skin laterally (see Figure 1.1). Do not remove skin. In reflecting the skin, gradually lift skin away from underlying tissue using a probe and/or a scalpel. Use special care in areas where blood vessels or nerves are running superficially.

NOTE: There will be varying thicknesses of adipose tissue depending on the nutritional characteristics of your cadaver. Some fat removal will be necessary and the underlying muscle will require clearing of fascia and adipose. Females will have more mammary tissue, most of which should remain intact on the skin side, and will be dissected for the reproductive laboratory.

FIGURE 1.1. Incision of Skin for Heart Dissection.

REMOVAL OF THE CHEST PLATE:

1. MUSCLE CUTS: Cut through the belly of the pectoralis major, reflecting flaps. Do the same for the pectoralis minor. (See Figure 1.2.) Label the muscles.

NOTE: It will be necessary to cut into and through smaller, related muscle groups. This is unavoidable but do not remove or discard muscle. (Adipose tissue may be discarded.)

2. BONE CUTS: (See Figure 1.3.) Using the bone saw or rongeur (bone-cutting pliers/clippers), cut through the manubrium at the site just inferior to the first or second rib attachment (A). Again using the bone saw or the clippers (whichever you find easier to handle), work downward from the second rib to the seventh rib (B). Work alternately from the left to right or vice versa, cutting carefully across each rib. The rib cuts should be made far enough laterally toward the mid-axillary line in order to excise the lung (a later assignment).

Use the scalpel and bone clippers only (not the bone saw!) beyond the fifth rib. The relaxed diaphragm projects up into this are and care must be taken to avoid cutting it. Continue in this manner with the horizontal cut (C) to the xiphoid process.

3. CHEST PLATE REMOVAL: Work from posterior cuts (6th or 7th rib) and progress anteriorly. Slowly and carefully lift alternate sides of the rib cage, cutting and teasing away connective tissue. Lifting the rib cage carefully is necessary to preserve the internal thoracic vessels, which run into the chest plate. Carefully excise the internal thoracics from the chest plate.

EXPOSING THE HEART:

[Heart in Situ] [Heart Anterior View] [Heart Posterior View] [Heart Postero-inferior View] 

NOTE:Keep the heart, lungs and mediastinum together.

1. Pericardial Sac: Stay superficial while opening the pericardial sac. Using surgical scissors, open the pericardium with an inverted-T incision and reflect back the flaps. (They can be pinned back.) Sponge or suction any fluid present. (See Netter, pp. 200-201.)

2. Coronary Vessels: (See Netter, pp. 204-207.) The heart will be surrounded by adipose. This fat must be carefully picked away using blunt dissection and tweezers to expose the vessels. It takes time. Locate the coronary arteries where they arise from the aorta. It will be helpful to refer to the atlases available in the lab for comparison with the cadaver and the location of various structures.

NOTE: DO NOT use a scalpel here as the coronary vessels can be superficial and are embedded in the adipose. Frequently, the vessels don't preserve well and can disintegrate in the fat. The interventriculars may descend into the myocardium and may not be as superficial as they appear in illustrations.

The heart must be lifted (without severing any vessels) to expose vessels on the dorsal side.

[Coronary Arteries Anterior] [Coronary Arteries Posterior]

3. Right Coronary Artery. Arises from the base of the aorta as it leaves the heart. The right coronary artery passes forward between the pulmonary artery and runs obliquely to the right side in the groove between the right atrium and ventricle. Subsequently, it curves around the right border of the heart, runs along its posterior surface as far as the posterior interventricular groove, where it then divides into two branches. One branch extends in a traverse direction, continuing in the groove between the right atrium and ventricle, and terminating in an anastomoses with the left coronary artery. The other branch descends and courses along the posterior interventricular furrow (posterior interventricular artery) until it anastomoses with the descending branches of the left coronary artery. The marginal artery extends as a branch off of the descending portion of the right coronary artery and extends toward the apex of the heart.

Left Coronary Artery. Arises from the left posterior sinus of Valsalva and passes forward between the pulmonary artery and the left atria-ventricular groove, where it divides into two branches. The transverse branch, known as the circumflex artery, passes outward in the left atrial-ventricular groove and continues around the left border of the heart to its posterior surface where it anastomoses with the transverse branch of the right coronary artery. The descending portion of the left coronary artery, known as the anterior interventricular artery, passes along the anterior interventricular groove to the apex of the heart where it anastomoses with the descending branches of the right coronary artery.

Great Cardiac Vein. Starts at the apex of the heart and ascends along the anterior interventricular groove to the base of the ventricles. Subsequently, it curves to the left side, between the left atrium and ventricle around to the posterior region of the heart, where it opens into the left extremity of the coronary sinus.

Middle Cardiac Vein. Starts at the apex of the heart and ascends along the posterior interventricular groove to the base of the heart where it terminates in the coronary sinus.

Coronary Sinus. This expanded portion of the great cardiac vein is situated on the posterior side of the heart within the atrial-ventricular groove. It is approximately one inch in length and appears as a prominent dilation. It receives the great and middle cardiac veins and may be covered by the muscular fibers of the left atrium.

STRUCTURES TO BE LABELED:

Pericardial Sac [Pericardial Cavity]

Right and Left Atria

Right and Left Ventricles

Superior and Inferior Vena Cavae

Pulmonary Artery and Vein

Aorta

Right and Left Coronary Arteries

Anterior and Posterior Interventricular Arteries

Circumflex Artery

Marginal Artery

Coronary Sinus

Ligamentum Arteriosum (Ductus Arteriosus) (if visible)

Great Cardiac Vein

Middle Cardiac Vein

Right and Left Auricles

REMOVAL AND INTERNAL DISSECTION OF THE HEART:

In order for students to understand cardiac function and blood flow, the interior of the heart must be closely examined. We will remove one cadaver's heart for this purpose, leaving the other intact. Choose the heart for removal that is more difficult to examine in situ.

Removal of the Heart:

Carefully sever the veins and arteries leading to and from the heart, leaving enough on both the heart and the chest to be recognized. At this point, it may be easier to identify and label structures that were difficult in situ. Label vessels as they appear on both the heart and in the thoracic cavity.

Internal Dissection: (See Netter, pp. 208-212)

[Right Atrium] [Right Ventricle] [Left Ventricle] [Left Atrium and Ventricle]

Locate the left auricle. Using a scalpel, cut into the outer wall of the auricle and down the left side toward the apex of the heart. Use your fingers to open the chambers as you cut in order to direct the scalpel. You should expose first the atrium, then cut through the bicuspid value, then open the ventricle. Once the chambers are opened, identify the cusps of the bicuspid value, the chordae tendineae, papillary muscles and trabeculae.

Do the same with the right side of the heart, noting that the right ventricle is more anterior than inferior to the atrium. Inside locate and expose the pulmonary and aortic semilunar values. Locate the opening into the right and left coronary arteries behind the aortic semilunar values. Also, find the coronary sinus opening beneath the superior vena cava in the right artrium.

DISSECTION OF THE JOINTS

The best way to do this is to visualize them by causing them to move. When you are ready to cut the muscle tendons, isolate each one by pulling and pushing on it and the muscle it attaches to. Then lift the tendon away from what lies beneath it, or place a ruler or other flat object to protect these structures when you cut it.

Before cutting too far, visualize the ligaments in the same way. Move the joint by flexing and extending or rotating the bones. The ligaments will tighten and curl and you will see exactly where they are. Flexion and extension works well to show the location of the medial and lateral collateral ligaments of the elbow and knee. To see the annular ligament of the elbow, rotate the radius by supinating and pronating the hand.

The joint capsule lies immediately beneath the major ligaments and produces the synovial cavity in which the articulation of bones occurs. To open the joint capsule, use scissors to make a horizontal incision through its middle anterior portion toward the medial and lateral sides. Contine the cut to completely encircle the joint. Make vertical cuts on the anterior and posterior surfaces to view structures within the joint cavity.

ELBOW JOINT -- ANTERIOR DISSECTION

1) A hinge joint, which is the portion between the trochlea of the humerus and the trochlear notch of the ulna.

2) The portion between capitulum of the humerus and the head of the radius, which is a gliding joint.

3) The portion where rotation takes place--between the circumference of the head of the radius and the radial notch of the ulna.

PROCEDURE: Place cadaver in supine position.

NOTE: 1) Beginning prosectors should review the bony features of the elbow region on a skeleton and in the atlas (for example, lateral and medial epicondyles of the humerus). (See Netter, p. 411.)

2) The prosectors should outline with a black marker initial incision lines on the cadaver's arm, allowing about six inches above and below the elbow (see Figure 2.1). On the completion of drawing lines, the prosectors can begin the skinning phase.

3) When cutting muscle tendons around the elbow, check with the instructor to see if you must leave the musculocutaneous, ulnar and median nerves intact and preserve the arteries (brachial, radial, ulnar) and veins (axillary, basilic). Review dissection of vessels of the arm (see Netter, pp. 414-422).

4) As prosectors reflect and cut deeper into elbow joint, care should be taken to open but not to destroy the joint capsule that encloses the synovial cavity.

5) Enough time should be allotted to complete the dissection in one sitting. Identification of ligaments is more difficult as they dry out.

Cut across the tendon of biceps brachii and bicipital aponeurosis and reflect the biceps brachii muscle towards its origin. Cut carefully the origin attachment of the pronator teres on the medial epicondyle of the humerus. On the lateral surface of the humerus, cut the origin attachment of the brachioradialis and extensor carpi radialis longus. Cut through the tendon of insertion of the brachialis and reflect muscle back towards its origin. Cut the insertion of the triceps brachii on the olecranon, medial side. The supinator muscle can be viewed now. Cut across the muscle's origin.

On the medial side of the joint, locate the ulnar collateral ligament, which is attached to both the humerus and the ulna. On the lateral side, detach the extensor muscles from the point of origin. Remove the supinator. Expose the radial collateral ligament, which fans from the lateral epicondyle to the annular ligament of the radius. The annular ligament encircles the head of the radius. The radius rotates freely in the annular ligament. Open the joint capsule anteriorly by making a transverse cut through the capsule between the ulnar and radial collateral ligaments. This exposes the synovial capsule.

IDENTIFY the joint capsule and the following ligaments:

Annular ligament--covers head of radius.

Radial collateral ligament (thumb side).

NOTE: One portion of this ligament blends with the annular ligament and another portion continues to the radius blending with fibers of the supinator muscle.

Ulnar collateral ligament.

NOTE: The anterior, posterior and oblique portions of the ligament.

LABEL the following ligaments:

Annular Ligament

Radial Collateral Ligament

Ulnar Collateral Ligament

IDENTIFY:

Articular Cartilage

Articular Capsule

FIGURE 2.1. Incising the Arm for Dissection of Elbow.

POSTERIOR ELBOW DISSECTION

Since this dissection is destructive to the surrounding tissue, it is best to use an arm that has already been dissected for another purpose. Once you complete this dissection, the surrounding area will not be good for illustrating anatomy in other areas such as veins and nerves.

With the cadaver lying in the prone position, locate the tip of the olecranon attached to the triceps and the medial epicondyle. If the area has not been skinned, expose the muscular layer of the arm from about 6 inches above the elbow to about 3 to 4 inches below the elbow. Around the end of the olecranon will be attached the triceps, the flexor carpi ulnaris and the tricipital aponeurosis. Leave the triceps attached to the olecranon. Shave down the medial side of the olecranon to remove the ulnar head of the flexor carpi ulnaris. Try to preserve the ulnar nerve ("funny bone") that runs between the medial epicondyle and the olecranon. (See Netter, pp. 414-422.)

On the lateral side of the olecranon, shave down the bone to remove the tricipital aponeurosis and the anconeus. Cut it and reflect it back. Cut the common extensor tendon and reflect it back to the lateral epicondyle. Now locate the trochlear notch of the olecranon, the C-shaped part of the bone curving around the capitulum of the humerus. Flex the arm and use the bone saw to cut through the olecranon to the trochlear notch. This cut should be about 1 inch down the olecranon from where the triceps attach to it. The olecranon will snap apart with its tip remaining attached to the triceps. The inside of the joint capsule will now be visible. Label the annular ligament and the joint capsule.

Remember to keep the area moist during the dissection.

KNEE DISSECTION

PROCEDURE:

Begin by making an incision 6 inches superior to the patella and continue downward 6 inches inferior to the patella. At the top and bottom of the vertical incision, make a horizontal incision. (See Netter, pp. 476-480.)

Carefully reflect the skin, working it away from the fat and muscle on the lateral and medial aspect of the leg. There are some superficial blood vessels lodged in the fat (great saphenous is one), so do not remove the fat at once with the skin. Carefully remove the adipose tissue, taking care not to cut the great saphenous that is located on the medial aspect of the knee, thigh and calf.

It will be necessary to remove excess connective tissue and demarcate the major muscle masses, taking care around the patella to define the quadriceps tendon, the lateral biceps femoris tendon, which inserts on the head of the fibula and lateral condyle of the tibia, and the medial semimembranosus tendon, which inserts on the medial condyle of the tibia. The biceps femoris and semimembranosus should be removed from the capsule except for about ½ inch proximal to their attachments. With the removal of biceps, the narrow fibular collateral ligament can be seen below the iliotibial tract insertion and should be cleaned. The tibial collateral ligament is a strong, flat band lying on the medial side of the joint under the tendons of the sartorius, gracilis and semitendinosus.

Immediately superior to the patella, make a vertical incision into the quadriceps tendon, cutting down to the bone. On each side of the patella, make a diagonal incision cutting through the lateral and medial patellar retinaculum, taking care not to cut the collateral ligaments, to create a flap containing the patella. Turn the flap down to expose the internal aspect of the patella. You will have to cut some of the iliotibial tract, but cut as little as possible. Carefully cut the infrapatellar synovial fold; this is a fat-filled fold of the synovial stratum, which runs from the lower back of the patella back to the inter-condyloid fossa of the femur. You will also have to cut some of the articular capsule in order to completely reflect the patella.

To expose the cruciate ligaments, it will be necessary to clear away the infrapatellar synovial fold and the fat contained in it. Remove excess fat and connective tissue around and within the knee joint. To expose the interior knee, prop the knee up on a block.

Define the anterior and posterior cruciate ligamentsbetween condyles. Locate and expose the medial and lateral menisci, which in older individuals may be absent. Locate and expose both medial and lateral menisci. (See Netter, pp. 478-479.)

STRUCTURES TO BE LABELED:

Patellar Ligament Anterior Cruciate Ligament

Quadriceps Tendon Posterior Cruciate Ligament

Fibular Collateral Ligament Lateral Meniscus

Tibial Collateral Ligament Medial Meniscus

POSTERIOR KNEE DISSECTION

While the anterior knee dissection gives a good view of the anterior cruciate ligament, the posterior knee dissection gives a good view of the posterior cruciate ligament, and the posterior side of the lateral and medial meniscus.

As with all joint dissections, it should be noted that clearing the joint for a good viewing of the ligaments results in the destruction of the surrounding tissue.

To skin the area, make a transverse incision across the crease of the knee and a perpendicular incision from the mid-thigh to the mid-calf. Clear away the adipose tissue from the back of the knee. The diamond-shaped popliteal fossa will be visible, which is the indentation seen at the back of the knee when flexed. Nerves, arteries and veins in this region need to be cut away to expose the area. Muscles also need to be cut and reflected back. If a muscle runs over the back of the knee, such as the biceps femoris or the semitendinosus, which insert on the tibia and fibula below the joint, it is best to cut the muscle above or below the knee in order to allow a better viewing of the joint.

On the lateral, posterior side of the lower end of the femur, the insertion of the lateral head of the gastrocnemius and the plantaris need to be shaved from the bone and reflected back. On the medial side of the lower posterior femur, the medial head of the gastrocnemius needs to be shaved from the bone and reflected back. The popliteus muscle and the oblique popliteal ligament must also be removed to give a good viewing of the joint. Now from this posterior aspect of the knee, the medial and lateral menisci and the posterior cruciate ligament can be labeled. Care when removing the joint capsule and associated tissues will allow you to find and label the menisofemoral ligament, which is just superficial to the posterior cruciate.

In each of the two illustrations below, one half of the femur is removed in sagittal section along with the proximal part of the corresponding cruciate ligament.

FIGURE 3.1. The posterior cruciate ligament prevents forward sliding of the femur, particularly when the knee is flexed.

FIGURE 3.2. The anterior cruciate ligament prevents backward sliding of the femur and hyperextension of the knee, and it limits medial rotation of the femur when the leg is fixed.

DISSECTION OF THE ANKLE JOINT and FOOT

SKIN INCISION:

Begin by making a 4-inch, vertical incision on the medial aspect of the ankle, cutting across the tibial malleolus down to the arch of the foot. Continue to cut horizontally toward the posterior side of the heel around to a point just below the fibular melleolus. As on the medial side, cut vertically upwards about 4 inches. Reflect the skin flap upward to expose the retinaculum and tendons of the lower leg muscles.

DELTOID LIGAMENT:

To expose the deltoid ligament on the medial side, simply splice the tendons of the tibialis posterior and flexor digitorum longus. You may find it easier to slide these tendons away from their position in the groove around the tibial malleolus. The deltoid ligament will fan downward from the inferior portion of the tibial malleolus to the talus of the foot.

OTHER POSTERIOR LIGAMENTS:

To expose the posterior inferior tibio-fibular ligament, transverse tibio-fibular ligament, and posterior talo-fibular ligament, sever the achilles tendon as well as the tendons of the peroneus longus and brevis below the level of the malleolus. These ligaments lie deep to the flexor hallucis longus muscle (which should now be in clear view) and run laterally toward the fibular malleolus. The calcaneo-fibular ligament also comes into view just inferior to the fibular malleolus once the tendons of the peroneus muscles are reflected away from that area.

DISSECTION OF THE BLOOD VESSELS OF THE HEAD, NECK AND ARM

NOTE: Generally, vessels will be exposed on one side only, with muscles dissected on the other side. Prior to attempting the dissection of the blood vessels of the head, neck and arm, pay close attention to the precautions in the chest dissection. The large veins of the superior chest region are easily damaged by the initial removal of the chest plate. Also, these veins are extremely flat and may be enmeshed in the supportive tissue of the chest. (See Netter, pp. 21-29, 402, 404, 406-409.)

If necessary, continue the upper chest incision that runs across the clavicles to the lateral side of the shoulder. Make an incision from the shoulder down the lateral aspect of the arm to the wrist. Ring the wrist. Make sure the skin incisions are very superficial, not extending into the fat because the cephalic vein is also very superficial. The cephalic vein runs in the groove between the pectoralis major and the deltoid. Gently reflect the skin from the arm starting at the shoulder. When reflecting the skin from the arm, be verycareful not to scoop the underlying fat out in large quantities. It is best to carefully pick out small fragments of adipose tissue as underlying blood vessels and muscle tissue may be damaged by overly aggressive adipose removal. Also, it is helpful to remember that most of the veins will be superficial compared to the arteries, and they are oftentimes much more flat and less noticeable. Veins found deeper within the arm may be firmly attached to connective tissue and mistakenly removed.

Continue the midventral incision on the chest anterior up the neck to the tip of the chin. Carefully reflect the skin anterior and lateral on the side not embalmed. Be verysuperficial because the external jugular vein lies close to the surface.

Make a midventral incision through the platysma from the sternal notch to the tip of the chin, being very careful not to cut any blood vessels. Detach the platysma from the clavicle on the side you have chosen (leave the other intact). Because the platysma is very thin, it may be reflected along with the skin by mistake, but this is fine since it is not needed.

With a bone saw or chisel, cut the remaining piece of manubrium in half with a midsagittal cut. Using the bone saw again, cut the clavicle distally at least two-thirds away from the manubrium. Carefully remove the piece of clavicle and manubrium by first detaching the muscles, then gently lifting from the sternum while cleaning away the connective tissue. When removing the clavicle, it would be easier to detach a segment slightly longer than the recommended length of two-thirds away from the manubrium. This will allow more room for your hands as you clear the connective tissue. Also, be careful when detaching the muscles from the sternum, and try to keep them as intact as possible in case they are needed in subsequent procedures.

Next, locate and clear around the arteries and veins. It doesn't matter whether you start with the neck or arm. It is easier to begin the clearing at the level of the superior chest and inferior neck since these vessels are most easily identifiable as they branch away from the heart. Subsequently, it is best to follow these large vessels through their smaller branches. This progression will reduce the amount of inadvertent vessel cutting.

When beginning the clearing of the arteries of the arm, try to keep as much of the musculature intact as possible; also be aware of and preserve nerves as you encounter them: the muscles and nerves of the arm may be used in subsequent dissections and it would be useful to maintain as much of their original form as possible. Of course, there may be some necessity to sever some of the muscle connections, particularly in order to locate the radial, ulnar and the interosseous arteries. However, these vessels can be located with complete removal of the overlying muscle tissue.

TERMS AND LOCATIONS:

Arteries:

Head and Neck: Beginning at the heart, define the branches of the aorta, brachiocephalic, left common carotid, and left subclavian. If you are working on the right neck and arm, follow the brachiocephalic to where it branches into the right common carotid and subclavian. Follow the common carotid (right or left) and find the carotid sinus, internal carotid and external carotid. Coming off the external carotid are three small, delicate arteries--the superior thyroid, lingualand facial. Going back to the subclavian, the next artery after the carotid is the vertebral. It frequently comes off the dorsal side of the subclavian, then runs deep passing through the transverse foramen of the cervical vertebrae. After the vertebral is a very small, fragile trunk leading to three arteries; this trunk is the thyrocervical trunk. Right before the subclavian passes under the clavicle, the last vessel can be found--the costalocervical trunk. Once the subclavian passes under the clavicle, it becomes the axillary.

Arm: The first vessel that comes off the axillary, at the anterior boarder of the pectoralis minor, is the thoracoacromial, which runs laterally. At the posterior boarder of the pectoralis, the subscapularisarises and runs deep toward the chest. Below this are the two parts of the circumflex humeral, which encircles the humerus. The lower part runs ventral to the teres major. Below this, the axillary turns into the brachial. At the level of the elbow is a major landmark--the bicipital aponeurosis. All arteries run underneath this, while all veins run on top. It is in this area that the brachial bifurcates into the radial and ulnar. Approximately 1 inch below the branch, the interosseous arises off the brachial and runs deep between the muscles of the forearm.

Veins:

Head and Neck: Beginning at the heart, clean off the brachiocephalics. Follow one on the side you have chosen until it branches into internal jugular and the subclavian. Off the dorsal side, the vertebral runs deep with the vertebral artery. Next, locate the external jugular arising from the subclavian.

Arm: Follow the subclavian until it crosses under the clavicle and becomes the axillary. The cephalic arises from the axillary and runs in the groove between the pectoralis major and deltoid muscles, becoming very superficial as it traverses the lateral aspect of the arm. The axillary branches into basilic and brachial. The brachial runs deep between the muscles of the upper arm and has many anastamoses. It is produced in the antecubitum by the joining of the radial and ulnar veins, which run in contact with the corresponding arteries. Careful stripping is needed to separate these vessels. The basilic is superficial and runs down the medial aspect of the arm to the wrist. At the level of the bicipital aponeuroses, a vessel connects the basilic to the cephalic; this the median cubital. Below this, a second vessel runs towards the middle of the lower arm; this is the median.

The structures to be cleaned and identified are designated above in bold, small capitals.

FIGURE 5.1. Arteries and Veins of the Neck and Arm.

DISSECTION OF THE MUSCLES OF THE HEAD, NECK AND BACK

NOTE: Generally, face and neck muscles will be dissected on one side only, with blood vessels dissected on the other side. Be sure to check with your instructor as to which sides to dissect.

To expose the masseter and temporalis muscle, make a skin incision starting at the chin, following around the mouth and up the side of the nose (Figure 6.1). The incision should stop at the top of the cheekbone, approximately a half an inch from the eye. The incision should then move vertically across the cheekbone (½ inch under the eye) to the end of the eye. Continue the incision horizontally close to the eye and stop about an inch above the temple. Also carefully remove skin from around one eye and around the mouth. Then take the cut vertically from above the temple even with the anterior part of the ear (do not go down toward the ear but only even with it). You may wish to "round" this entire cut to better expose the origin of the temporalis (Figure 6.2). If the chest dissection has been done, it will not be necessary to cut vertically across the jawbone since the skin flap will already be done there; however, if it has not been done, continue the incision from the chin to the posterior part of the ear following the angle of the jawbone. Keeping the skin as one flap, retract the flap slowly, separating the skin from the fat until the flap can be pulled back over the ear. The flap should be attached at the points above and below the ear (two inches from the top of ear and one inch from the bottom). This type of incision allows for easier closure over the face and better protection from drying out. One will encounter difficulty in reflecting only the skin from the face because the superficial muscles of the face insert into the skin. You may shave off these attachments. The temporalis is below several layers of subcutaneous fascia and covers the side of the head. The masseter is attached to the skull and jaw and is embedded in the fat of the cheek. Be careful removing the fat because the parotid gland and duct lie over the masseter and need to be left intact for later identification. Once the fat has been removed, the masseter should be relatively easy to see. (See Netter, p. 19.)

MUSCLES OF THE CHEST:

On the chest plate, expose the external and internal intercostals by clearing away fat and connective tissue on the outside and inside of the plate.

STRUCTURES TO BE LABELED:

Masseter

Temporalis

Platysma

Orbicularis oris

Orbicularis oculi

Sternoclidomastoid

Pectoralis major

Pectoralis minor

Internal & external intercostals

FIGURES 6.1 & 6.2. Incision of the Face.

MUSCLES OF THE BACK AND POSTERIOR OF THE NECK: (See Netter, pp. 160-164, 399-401.)

Starting at the base of the skull, make a midsagittal incision to the upper level of the sacrum. Continue the incision lateral on both sides to the iliac crest. In the neck area, make lateral incisions from the external occipital protuberance to the back of the ear, and across the upper back from the vertebral column to the shoulder.

Dissection of the back and neck muscles will be done in four levels. You may adhere to the following plan, or you may select which muscles are to be dissected on which cadavers and in which layers, as you see fit. Your plan should evolve as the dissection proceeds in order to make best use of what is available. There will be two levels to the superficial dissection and two for the deep, a TOTAL OF FOUR SIDES to be dissected.

SIDE 1:

Side 1 is going to be either the right or the left side of the body (either side of the midsagittal incision). Retract the skin back on the one side. This is the most superficial. Leave the complete latissimus dorsi and trapezius. Clean the trapezius by removing the superficial and deep fasciae that cover its entire external surface. When cleaning the upper lateral border of the muscle, be careful to preserve structures on the posterior region of the neck. The trapezius is a flat, triangular muscle. Its fibers converge laterally to a V-shaped insertion on the posterior border of the lateral third of the clavicle, the medial border of the acromion, and the upper border of the scapular spine.

Clean the latissimus dorsi. In removing the superficial fascia from the region just lateral to the lumbar vertebral spines, carefully avoid cutting through or removing the deep fascia known as the thoracolumbar fascia. The lumbar region of the back is covered with a thick layer of fat that must be removed. The thoracolumbar fascia is directly below the fat and is recognized by the glistening aponeurotic appearance of its external surface. It attaches medially to the lumbar and sacral spines and stretches laterally as a broad aponeurotic sheet.

STRUCTURES TO BE LABELED:

Latissimus Dorsi

Trapezius

SIDE 2 (Deep Muscles of the Back):

Side 2, the trapezius and latissumus dorsi, is going to be the opposite side of the midsagittal incision of the side you just finished working on. Retract the skin back on this side. Carefully remove (or reflect back) the latissimus dorsi and trapezius by cutting them at or near their insertions. For the trapezius, cut the insertion along the scapular sprine, acromion and clavicle. However, before these muscles are removed, insert a finger beneath the muscle and palpatate it and the nearby structures. This is done to avoid cutting through adjacent structures, since the thickness of the muscle to be removed cannot be fully appreciated until it is palpitated. Be careful when removing the trapezius at the occipital bone and along the ligamentum nuchae because the splenius capitus lies just beneath this muscle and also attaches to the ligamentum nuchae. Also remember that the semispinalis capitis inserts on the occipital bone as well, so be cautious when removing the trapezius from there.

Clean the two rhomboid muscles. They are sometimes more or less fused. The rhomboideus minor is narrow; the rhomboideus major is much wider and is immediately inferior to the minor.

To display the splenius, detach the sternocleidomastoid from the occipital bone to within an inch of the tip of the mastoid process and turn it laterally. Clean the levator scapulae. This is a long, flat muscle that inserts into the vertebral border of the scapula above the scapular spine. The splenius capitus has the same upper attachments as the sternocleidomastoid. On some cadavers, the posterior muscle of the neck and the deep muscles of the back will be fused and it will be very hard to differentiate one muscle from another. Extreme patience and caution must be used to display these muscles.

STRUCTURES TO BE LABELED:

Semispinalis Capitus

Splenius Capitus

Levator Scapulae

Rhomboid Major Rhomboid Minor

Deltoid

Teres Major

Teres Minor Infraspinatus

Supraspinatus

Serratus Anterior

SIDE 3:

Reflect the latissimus dorsi and trapezius. (An alternate method might be to cut the trapizius, leaving its origin intact.) Remove the rhomboid major and minor. Remove the splenius capitus to expose the longissimus capitus and semispinalis capitus. You should be able to see the levator scapulae. Remove the deltoid from the scapula.

The sacrospinal lies exposed once the latissimus dorsi is reflected. The sacrospinalis has three columns--lateral, intermediate and medial.

STRUCTURES TO BE LABELED:

Longissimus Capitus Teres Major

Semispinalis Capitus Teres Major

Levator Scapulae Erector spinae

SIDE 4:

Detach the trapezius from the occipital bone, acromion and scapular spine, and from the clavicle. Reflect the trapezius back. Detach the latissimus dorsi from the vertebral attachments. Detach the rhomboids from the scapula.

STRUCTURE TO BE LABELED:

Subscapularis

DISSECTION OF THE BLOOD VESSELS OF THE LEG

The skin incision should be made down the lateral aspect of the leg, being very superficial in the ankle area. Ring the ankle. Work the skin flap off (leaving the fat on the leg), starting at the ankle. Take care to preserve the saphenous veins (great and small). These are verysuperficial and are likely to pull away with the skin. Should this happen, pull them away from the skin as you go. If one should break, you can suture the ends back together. In the inguinal area, make an incision from the lateral incision across the inguinal ligament to the pubic bone. Make sure this incision is very superficial in order to preserve the epigastric vein and the spermatic cord (if applicable).

Branching from the abdomina aorta and inferior vena cava, respectively, are the common iliac artery and vein. If the abdomen has not been opened, leave these vessels until that time.

The external forms the femoral and deep femoral artery and vein.

The epigastric comes off the external iliac and goes up.

The great saphenous comes off the femoral vein and runs medially.

The medial circumflex artery comes off the deep femoral and goes under the femoral vein.

The medial circumflex vein comes off the femoral vein before the deep femoral branches off.

The lateral circumflex artery comes off after the deep femoral branches off.

The lateral circumflex vein lies just below the lateral circumflex artery and comes off at the femoral/deep femoral branch.

CLEAN, IDENTIFY AND LABEL the following vessels:

Arteries and Veins:

Common Iliac Artery Common Iliac Vein

Internal Iliac Artery Internal Iliac Vein

External Iliac Artery External Iliac Vein

Femoral Femoral

Lateral Femoral Circumflex Lateral Femoral Circumflex

Medial Femoral Circumflex Medial Femoral Circumflex

Deep Femoral Deep Femoral

Great Saphenous

Epigastric

POSTERIOR DISSECTION: (See Netter, pp. 472-473, 485-487.)

Begin at the lumbosacral area with an incision extending to the most lateral aspect. Turn the incision perpendicular and continue the incision down the lateral aspect of the thigh to the ankle. Ring the ankle. Carefully work the skin away from the adipose and muscle on the whole posterior aspect of the leg. Do not remove the adipose with the skin. It is best to work slowly to preserve all vessels and nerves that lie in the fat.

Locate the gluteus maximus. Remove the gluteal aponeurosis that connects the anterior edge of the muscle to the iliac crest. Lift up the edges of the muscle, working all adipose and connective tissue away from the muscle. Deep blood vessels and nerves adhere to the muscle above them, so, as the muscle is raised, identify the piriformis. The superior gluteal arteries are usually found attached to the underside of the gluteus medius. The inferior gluteals are attached to the underside of the gluteus maximus. Once vessels are revealed, they can be removed from the muscles and, depending on the circumstances, muscles may be removed entirely; check with the instructor.

The posterior femoral cutaneous nerve is found closely adhering to the skin on the posterior medial thigh. It must be preserved for later dissections. The femoral vessels arise through the adductor hiatus.

The femorals become popliteals as they approach the popliteal fossa. Carefully remove the adipose tissue to demarcate the muscle borders. With this done, the popliteal vein should be visible. If not, clean out the popliteal fossa of adipose and connective tissue. Now the popliteal vein should be visible. Directly underneath this is the popliteal artery.

Follow the medial aspect of the popliteal artery anterior and posterior. The genicular arteries come off the popliteal in the knee area and completely enclose the knee.

The popliteals bifurcate into anterior and posterior tibials. The posterior tibial gives rise laterally to the peroneal. On the lower leg, the gastrocnemius and soleus muscles, or other origins, must be bisected and retracted to allow access to the peroneal and posterior tibial artery and veins. Locate the anterior tibial vein and artery that originate from the popliteal and run through the space between the tibia to the anterior aspect of the leg. Locate the peroneal artery that runs deep toward the middle of the leg. Arising from the popliteal vein in the area of the back of the knee is the small saphenous, which may have to be cut to allow access to the peroneal and posterior tibial vessels.

CLEAN, IDENTIFY AND LABEL:

Arteries and Veins:

Superficial: Genicular Artery Genicular Vein

Genicular Popliteal

Femoral Small Saphenous

Popliteal

Deep: Superior Gluteals Superior Gluteals

Inferior Gluteals Inferior Gluteals

Posterior Tibial Posterior Tibial

Anterior Tibial Anterior Tibial

Peroneal

May also be seen in anterior dissection.

DISSECTION OF THE MUSCLES OF THE ARM, ABDOMEN, CHEST AND PELVIS

The skin has most likely been reflected from a previous dissection; if not, see p. 19 for directions. It will now be necessary to extend the lateral incision to the distal joint of the thumb. The skin will have to be removed from the palm as well as the back of the hand. Try to isolate and preserve the dorsal and, especially, the ventral retinaculum. The ventral retinaculum forms what is known as the "carpal tunnel."

Remove the fat and connective tissue to expose muscle insertions, origins and bodies. Many of the muscles of the arm are over-layered. Use a blunt probe to separate, identify and prepare to label. It is beneficial to first begin by cleaning the fat and connective tissue from the hand and fingers. Preserving the nerves and blood vessels are up to the prosector's discretion. Once the hand and fingers have been cleaned, the tendons in the hand can be used to identify the flexors and extensors in the forearm. Human Anatomy and Physiology by N. Marielb is a very good reference for identifying the muscles of the arm and abdomen.

The following are the muscles that need to be labeled:

Coracobrachialis--Covers a portion of the upper medial surface of the humerus. Origin: apex of the coracoid process of the scapula. Insertion: near the middle of the medial surface of the humerus.

Biceps brachii--Large muscle on the anterior portion of the humerus. Origin: 1) medial tendon attached to the coracoid process and 2) lateral tendon fits into a groove on the humerus. Insertion: radial tuberosity.

Brachialis--Immediately under the biceps brachii on distal anterior portion of the humerus. Origin: lower half of the humerus. Insertion: attached to the front of the coronoid process of the ulna.

Brachioradialis--Origin: lateral epicondyle of the humerus and the upper two-thirds of the supracondylar ridge. Insertion: styloid process of the radius.

Triceps brachii--Posterior surface of the upper arm. Origin: 1) from scapula, 2) posterior surface of the humerus, and 3) below the radial groove. Insertion: the olecranon process of the ulna.

Supinator--Origin: lateral epicondyle of the humerus and the ridge of the ulna. Insertion: lateral edge of the radial tuberosity.

Pronator teres--Origin: medial epicondyle of the humerus. Insertion: upper lateral surface of the radius.

Pronator quadrator--Origin: distal half of the ulna. Insertion: distal lateral portion of the radius.

Anconeus--Origin: lateral epicondyle of humerus. Insertion: lateral aspect of olevanon process of ulna.

Flexors of the carpus--Identify individually.

Flexor carpi ulnaris--Origin: medial epicondyle and olecranon process. Insertion: carpal/metacarpals.

Flexor carpi radialis--Origin: medial epicondyle of humerus. Insertion: base of second and third metacarpals.

Palmaris longus--Origin: medial epicondyle of humerus. Insertion: palmar aponeurosis.

Flexors of the digits--Identify individually.

Flexor digitorum superficialis--Origin: medial epicondyle, coronoid process and anterior border of radius. Insertion: middle phalanges of digits.

Flexor digitorum profundus--Origin: proximal two-thirds of ulna and interosseous membrane. Insertion: distal phalanges.

Extensors of the carpus--Identify individually.

Extensor carpi radialis longus--Origin: lateral supracondylar ridge of humerus. Insertion: second metacarpal.

Extensor carpi radialis brevis--Origin: lateral epicondyle of humerus. Insertion: third metacarpal.

Extensor Carpi Ulnaris--Origin: lateral epicondyle of humerus and posterior border of ulna. Insertion: base of the fifth metacarpel.

Extensors of the digits--Identify individually.

Extensor digiti minimi--Origin: lateral epicondyle of humerus. Insertion: extensor aponeurosis of fifth digit.

Extensor digitorum--Origin: lateral epicondyle of humerus. Insertion: posterior surfaces of phalanges II-V.

Flexor pollicis longus--Origin: radius and ulna. Insertion: attached to the distal phalanx of the thumb.

Extensor pollicis brevis--Superior to the longus muscle. Insertion: proximal phalanx of the thumb.

Extensor pollicis longus--Extends from the ulna to the end of the thumb. Origin: posterior surface of the radius and ulna. Insertion: distal phalanx of the thumb.

Abductor pollicis--Found on the dorsal side of the thumb. Origin: interosseous ligament between the radius and ulna. Insertion: lateral portion of the metacarpal and trapezium.

ABDOMINAL MUSCLES (including those of the chest and pelvis): (See Netter, pp. 232-235.)

The skin incision should be made midventrally beginning at the chest incision extending down to the pubic bone. Two lateral incisions should be made from midpubis lateral to the iliac crests (Figure 8.1). Be very superficial in these skin incisions over the inguinal ligaments because the epigastric veins and spermatic cords lie in the fat directly below the skin in this area. Reflect the skin back. Once the skin is reflected, the external oblique is visible (Figure 8.2). The rectus abdominal is covered by the aponeurosis.

Leaving one side intact, carefully cut and peel back the aponeurosis and expose the rectus abdominus. Then, carefully separate the external oblique from the internal oblique (Figure 8.3). These muscles lie one below the other so don't use a scalpel or make a deep cut. When the internal and external are separated, trim the aponeurosis around the external, leaving a border about 1 inch deep. Flap it back to expose the internal.

Separate the internal oblique from the transverse abdominal (Figure 8.4). Again, use caution so as not to cut through the muscle. Trim the aponeurosis from the internal oblique and flap it back to expose the transverse abdominis. Label these four muscles.

NOTE: Do not separate the transverse abdominis from the parietal peritoneum.

Clean further, if necessary, and LABEL the following muscles exposed previously:

pectoralis major

pectoralis minor

external intercostals

internal intercostals (by removing a small section of the externals)

Once the abdominopelvic cavity is opened, the iliacus and psoas major muscles should be labeled as well.

FIGURES 8.1­4. Exposing the Abdominal Muscles.

DISSECTION OF THE RESPIRATORY SYSTEM

(See Netter, pp. 68-75, 182-189.)

DISSECTION USING ONE CADAVER:

Using a scalpel, cut either the right or left primary bronchus about half way between its bifurcation from the trachea and the root of the lung. If the incision is made too far laterally, you will be cutting through the secondary bronchi. Also cut through the pulmonary artery and pulmonary veins in the same fashion.

You should now be able to remove the lung from the chest cavity. Looking at the lung, you should see the pulmonary artery, primary bronchus and two pulmonary veins. Use tweezers to carefully clean around the pulmonary artery, primary bronchus and two pulmonary veins. (Once the lung has been completely removed and dissected, place it in a plastic bucket with fluid to preserve it.) (See Alternate Dissection and Internal Dissection, below.)

Taking care not to damage blood vessels or nerves, all the muscles of the neck must be removed to expose the hyoid bone, larynx and trachea. (Preserve the thyroid gland that lies interior to the cricoid cartilage, which lies at the apex of the thyroid cartilage.) You may also hinge or remove the clavicle. Cut superior to the hyoid bone and use a scalpel and blunt dissection to separate the larynx, trachea and esophagus from the posterior body wall. You can then "hinge" these structures anteriorly and view down into the glottis, observing the epiglottis and true and false vocal cords as well.

The thyroid and cricoid cartilages must be cleared of muscle and connective tissue to be clearly visible. Muscles of the hyoid bone must also be removed. Make an anterior, midline incision through the thyrohyoid membrane, thyroid cartilage, cricothyroid membrane, cricoid cartilage and the first three tracheal rings (this may require cutting through the isthmus of the thyroid gland). By spreading the larynx and trachea, you should be able to see vocal folds and the epiglottis.

Once all of these structures are opened and visible, LABEL them as follows:

Pulmonary artery Vocal folds (true vocal cords)

Primary bronchus Epiglottis

Pulmonary vein Cricoid

Thyroid cartilage Trachea

Thyroid gland Vestibular folds (false vocal cords)

Hyoid bone

DISSECTION USING TWO CADAVERS:

The respiratory tract from one cadaver will be completely removed. Do this in the same cadaver from which the heart has been removed. Isolate the larynx, hyoid bone an trachea as in paragraph 3 above. Cut and remove the remaining pericardium and other connective tissue as well as portions of the pulmonary arteries and veins as neccessary to free the respiratory tract. Cut the esophagus away from the larynx and pull the lungs, trachea and larynx out of the thorax.

The anterior sagittal section described in paragraph 4 above should be done on the larynx, which remains in the cadaver. On the excised lung, make a similar sagittal section from the posterior side to reveal the vocal folds and epiglottis. Dissect the lung as described below.

INTERNAL DISSECTION:

Carefully remove lung tissue from one lung, exposing the secondary and tertiary bronchi within one or two lobes. Cut tissue away from the surfaces of the passageways, going as far as you can along one branch of the respiratory tree. The cartilages should be evident as well as openings into arteries, veins, etc.

DISSECTION OF THE MUSCLES OF THE LEG

(See Netter, pp. 460-465, 484-491, 497-499.)

SKIN INCISION:

Make initial incision on lateral side of leg from iliac crest to ankle, making a ring around the ankle. For the front dissection, continue incision from anterior superior iliac spine medially, extending incision as is necessary to expose inguinal region. For back dissection, make a bow-shaped cut medially from the cranial end of incision following around iliac crest to the midline. PLEASE NOTE that in the inguinal region the spermatic cord, epigastric and great saphenous veins are superficial. Below the knee the small saphenous vein and common superficial peroneal nerves are superficial also. Additionally, remove the skin from the ankle and foot to expose the muscle tendons. Remove the skin in such a way that it can be used to keep the foot from drying out, or use a plastic bag and gauze.

Start laterally working the skin back medially, leaving as much fat as possible on the leg. This will make it easier to go back and carefully remove the fat layer so as not to damage the aforementioned structures.

After removing the fat, begin to remove the deep fascia. It will run somewhat diagonally on the leg. Start at about midrectus femoris and work laterally and medially. Carefully clean the knee area, watching for all the tendon insertions.

FRONT MUSCLES:

The front muscles are described laterally to medially. IDENTIFY, CLEANand LABEL the following muscles:

Iliotibial tract--This is a broad tendon that arises from the iliac crest and aponeurosa of the gluteus maximus and attaches to the upper half of the tibia laterally and inferiorly to the patella. The tract will be markedly thicker than the deep fascia and its fibers will only run vertically on the lateral thigh. It ensheathes the tensor fasciae latae muscle.

Tensor fasciae latae--Originating behind and below the anterior superior iliac spine and the anterior outer lip of the iliac crest, it inserts between the two layers of the iliotibial tract, a band of the fascia lata. This band is a thickening of the external fascia of the thigh called the fascia lata (broad fascia).

Vastus lateralis--Originates from the lateral aspect of the linea aspera and inserts onto the patella via the quadriceps tendon.

Rectus femoris--Lies between the vastus lateralis and the vastus medialis, in the middle of the thigh. This muscle originates from two tendons: one from the anterior inferior iliac spine and the second from the groove just above the acetabulum. It inserts onto the base of the patella as part of the quadriceps tendon.

Vastus intermedius--Lies deep to the rectus femoris and arises from the anterior and lateral surfaces of the shaft of the femur and inserts via the quadriceps tendon on the base of the patella.

Vastus medialis--Lies medial to the rectus femoris, originating from the inter-trochanteril line and medial linea aspera of the femur. It also inserts onto the patella via the quadrips tendon.

Sartorius--Crosses the thigh as a superficial muscle originating from the anterior superior spine of the ilium and inserting on the medial surface of the body of the tibia; makes up the lateral border of the femoral triangle.

Adductor brevis--Lies deep to the adductor longus; originates from the inferior pubic ramus of the pubis and inserts onto the medial linea aspera of the femur above the adductor longus.

Adductor longus--The most superficial of the three adductors; originates from the front of the pubis near the symphysis and makes a fan-shaped insertion onto the medial linea aspera of the femur between the adductor magnus and the vastus medialis (see below).

Adductor magnus--Located at the medial side of the thigh, this muscle originates from the inferior ischiopubic ramus and inferior ischial tuberosity, inserting onto the medial linea aspera of the femur.

Gracilis--The most medial superficial muscle, it originates from the inferior ramus of pubis and inserts on the medial surface of the tibia below the medial condyle.

Below the knee:

Peroneus tertius--Lies just medial to the lateral malleolus, usually continuous and fused with extensor digitorum longus, and not always present. It originates from the distal front fibula and interosseous membrane; its tendon passes anterior to the lateral malleolus and inserts onto the dorsum of the fifth metatarsal.

Extensor digitorum longus--Originates in three parts: from the lateral condyle of the tibia, from the anterior surface of the fibula and from the interosseous membrane. This muscle inserts onto the superior surfaces of the middle and distal phalanges of the lateral four toes.

Extensor hallucis longus--Originates from the middle anterior surface of the fibula and the interosseous membrane. It inserts onto the superior and basal surfaces of the distal phalanx of the big toe.

Tibialis anterior--Originates from the lateral condyle and upper two-thirds of the tibia and inserts onto the inferior surfaces of the first cuneiform and first metatarsal.

DORSAL MUSCLES:

Before doing this dissection, refer to the back leg dissection of the peripheral nerves and note their location, especially the posterior femoral cutaneous nerve. Then, carefully remove the skin, fat and deep fascia from the posterior leg, and again demarcate the iliotibial tract and label it. In order to expose the deep muscles in the buttocks, the following dissections need to be performed.

Gluteus Maximus Bisection:

Once the skin and fat have been removed, the gluteus maximus will have to be cut. But before this can be accomplished, the superior and inferior borders will need to be separated and freed from the fascial connections. Note the positioning of the gluteus maximus. It runs from the sacral region inferiorly and obliquely to the iliotibial tract. Above the oblique, the superior border of this muscle will be the fascia covering the gluteus medius, which lies underneath. Once freed, bisect the superior border of the gluteus maximus about midway between the insertion and origin, and continue the cut inch-wise by spreading apart tissue and examining (by palpating or visual examination) for blood vessels or nerves prior to each cut. When it becomes too difficult to visualize what is underneath, stop and begin a cut starting from the inferior border. Begin this cut by first following the sciatic (and posterior femoral cutaneous) nerve as they run underneath the lower border of the gluteus maximus. The purpose of this is to prevent unnecessary destruction of tissue while orienting the dissector. Extend the cut from the inferior border while following the nerve, being careful not to cut what is ambiguously visualized. The sciatic will continue up under the muscle and dive into the greater sciatic foramen just underneath the inferior border of the piriformis (in about 87% of cases). Continue the inferior cut in this fashion until it meets the superior cut. Carefully clear the fat and fascia from under the flaps, taking care not to sever the underlying arteries, veins and nerves. Clean and label these structures before continuing.

Gluteus Medius Bisection:

Normally, bisecting this muscle is optional since the gluteus minimus can be seen by simply pulling aside the gluteus medius. However, in a classroom situation, the muscle will be handled so often that it is better to cut this muscle also. As above, the cut needs to be at about midway between origin and insertion (so that both can be visualized by the student). The superior gluteal artery and nerve are clearly visible under the superior border of the piriformis and will have to be identified and labeled if they will be needed later.

IDENTIFY, CLEAN and LABEL the following musculature:

Gluteus maximus--Originates from the ilium, sacrum and coccyx, and inserts onto the iliotibial tract and the gluteal tuberosity of the femur.

Gluteus medius--Lies deep to gluteus maximus; it originates from the outer surface of the ilium and inserts onto the lateral surface of the greater trochanter of the femur.

Gluteus minimus--Deep to gluteus medius, it originates from the external surface of the ilium and inserts onto the anterior border of the greater trochanter.

Piriformis--Lies inferior to gluteus minimus; it originates from the anterior surface of the sacrum and inserts onto the upper border of the greater trochanter.

Quadratus femoris--Lies inferior to the piriformis, obturator internus and gemelli muscles and deep to the sciatic nerve. It originates from the ischial tuberosity and inserts into the greater trochanter. It is one of a group of six deep, lateral rotators of the thigh (the other five include, from superior to inferior, the piriformis, superior gemellus, obturator internus, inferior gemellus, and obturator externus).

Biceps femoris--On the posterolateral side of the thigh, it originates from the ischial tuberosity, linea aspera and distal femur; its tendon inserts onto the head of the fibula and lateral condyle of the tibia.

Semitendinosus--Lies medial to biceps femoris; it originates from the lower medial ischial tuberosity and inserts onto the upper portion of the shaft of the tibia.

Semimembranosus--On the medial side of the thigh, it originates from the upper outer ischial tuberosity and inserts onto the posteromedial portion of the medial condyle of the tibia.

The deep muscles of the calf may be visible on the lateral and medial sides of the gastrocnemius and soleus. If not, perform the following bisection.

Gastrocnemius/Soleus bisection--Both these muscles require cutting to see the underlying musculature (e.g., tibialis posterior, flexor hallucis longus and flexor digitorum longus). To do this, cut the gastrocnemius at about two-thirds up the muscle near the medial and lateral heads. In a similar fashion, the soleus is also cut near (but not at) its origin. (In between the two muscles is a small slender muscle that is sometimes lost, the plantaris. The belly is found high, under the heads of the gastrocnemius; it originates from the linea aspera and oblique popliteal ligament; it inserts onto the calcaneus.)

After reflecting the soleus, slit the loose intermuscular septum to give access to the tibial nerve as well as the posterior tibial vessels and the deep muscles of the posterior compartment.

CLEAN, IDENTIFY and LABEL the following calf muscles.

Peroneus longus--Lies lateral to the proximal portion of the flexor hallucis longus. This muscle originates at the head and upper two-thirds and deep fascia of the fibula, and inserts onto the proximal portions of the first cuniform and first metatarsal.

Peroneus brevis--Under the peroneus longus tendon, lateral to the centrally located flexor hallucis longus, this muscle originates from the intermuscular septa and the distal two-thirds of the fibula. It inserts onto the proximal end of the fifth metatarsal.

Flexor hallucis longus--The most lateral of the flexors. This muscle originates from the lower two-thirds of the fibula and interosseous membrane, and inserts onto the base of the distal phalanx of the big toe.

Soleus--Originates from the heads of the fibula and tibia. It inserts into the achilles tendon, which, in turn, inserts at the calcaneus.

Gastrocnemius--Originates from the posterior surfaces of both the medial and lateral condyles of the femur, and inserts by a tendon which combines with the soleus tendon to form the tendon of Achilles (tendocalcaneus).

Tibialis posterior--Lies deep to soleus bipennate and deep to the two flexors, which lie on either side; this muscle originates at the interosseous membrane, fibula and tibia. It inserts into the inferior surfaces of the navicular, cuneiform, cuboidal, and second, third and fourth metatarsal.

Flexor digitorum longus--The most medial of the flexors, this muscle originates from the fascia covering the tibialis posterior and from the posterior portion of the tibia, and inserts onto the bases of all the distal phalanges with the exception of the big toe.

If tendon insertions need to be seen to identify the muscles, the following foot dissection may need to be performed:

Skin Incision:

Most of the tendons of the lower leg muscles can be seen in areas posterior and anterior to the lateral and medial malleolus. Skin incisions can vary as the prosector prefers in providing access to these areas. The following is a descriptive list of the lower leg muscle insertions by compartments.

Lateral Crural Compartment:

This dissection occurs posteriorly to the lateral malleolus. Portions of the superior peroneal retinaculum and the inferior retinaculum will need to be cut in order to expose the tendon of the peroneus brevis and peroneus longus as it travels to the fifth metatarsal. Clear away tissues from the peroneus longus tendon to the point where it disappears into the sole of the foot.

Anterior Crural Compartment:

This dissection occurs on the dorsum of the foot. Anterior to the ankle and starting from the medial side, locate the tendons of the tibialis anterior, extensor hallucis longus and extensor digitorum longus moving toward the lateral side.

NOTE: The superficial peroneal nerve, which innervates the lateral crural compartment, lies along the anterior border of the peroneus brevis and continues to the dorsum of the foot.

NOTE: The deep peroneal nerve, which innervates the anterior compartment, sends out a small cutaneous branch that emerges between the first and second toe.

Posterior Crural Compartment:

This dissection occurs at the medial malleolus. The tendon of the flexor digitorum longus passes along the medial border of the sustentaculum tali (a bony landmark). The tendon of the tibialis posterior passes above this landmark. The tendon of the flexor hallucis longus disappears into an osseofibrous tunnel that runs in a groove below the sustentaculum tali.

NOTE: Even though the flexor digitorum longus lies medially, it is inserted into the four lateral toes. Similarly, the flexor hallucis longus lies laterally in the posterior compartment, but is inserted into the big toe. Therefore, these tendons cross each other.

DISSECTION OF THE SPINAL CORD

If not already done, the skin incision should be made in the following manner. A midventral incision should be made beginning at the base of the skull that extends down to the sacrum. On either side, make two lateral incisions. One incision should transverse the distal border of the shoulder, the other should extend laterally from the sacrum to the lateral aspect of the leg.

SPINAL CORD:

The primary task is to expose spinal ganglia. The superficial, intermediate and deep muscles of the back must be retracted 5-6 inches on either side of the spinous process for each vertebra. Incise through the muscle just lateral to the dorsal spinous process and retract. With toothed forceps, carefully pick the muscle from between vertebrae and ribs laterally for about two inches. CAUTION: Leave exiting nerves intact as they are embedded within the muscles.

Beginning in the L3-L5 region, remove the spinous process from each vertebra as described below. CAUTION: For the first one, go slowly and carefully using bone saw, rongeurs or knife, taking care to avoid nerve damage. (Also, by starting below L3, the cord should be absent, thereby lessening the danger.)

Using a chisel, knife or bone saw, carefully make a lateral cut on either side, right against the transverse process. (See Cut #1, Figure 11.1). Next, make two transverse cuts superior and inferior to the spinous process. Go only deep enough to separate the processes; any deeper could cross-section the cord.

Now, by grasping the spinous process, remove the rectangular piece of bone. Use a flexible, thin tool, such as a plastic ruler or small forceps, to stick in between the dura mater and bone for protection of the spinal cord, and use the same procedure to remove part of the next vertebrate (see Figure 11.1). Carefully continue superiorly and inferiorly until the spinal cord is exposed from skull to approximately S5, exposing the conus medullaris, filum terminale and cauda equina. CAUTION: In the cervical region and fused sacrum, the bone is very thin. Cut or chip away the superficial bone of the sacrum to expose the nerves.

Next, again using your thin tool for protection, the bone saw or knife can be used to cut through the articular processes to expose the spinal ganglion on each side. These cuts are transverse ones to open a slot around the spinal ganglion and exiting nerve, but do not separate the ribs from their attachment to the vertebrate. Alternatively, the entire side of vertebra can be romeved, including processes, in order to see some or all of the emerging nerve roots. After removing the bone, the fatty tissue surrounding the spinal ganglion and dura mater can be exposed. The exposed dura mater is carefully incised on the dorsal midline. The arachnoid mater can be observed just under the dura mater. Opening the subarachnoid space, the pia mater can be seen covering the surface of the spinal cord. On each side, the pia mater forms strong tendon-like connections with the dura mater called the denticulate ligament. At the end of the cord, between L₁ and L₂, is the conus medularis. The cauda equina makes up the collection of ventral and dorsal roots caudal to the termination of the spinal cord. The filum terminale is the pia mater extension following the end of the spinal cord, which continues down the vertebrate column to anchor at the coccyx.

Clean and expose the cord and BE ABLE TO LOCATE THE FOLLOWING STRUCTURES:

Arachnoid Mater Denticulate Ligament

Pia Mater Ventral and Dorsal Roots

Spinal Ganglion Spinal Nerves

Dura Mater Conus Medularis

Filium Terminale Cauda Equina

Epidural Space Subdural Space


FIGURE 11.1. Spinal Cord

DISSECTION OF THE GASTROINTESTINAL SYSTEM

NOTE: During this dissection it is important to preserve the blood vessels of the abdomen. To prevent their destruction, it is advisable to become familiar with their locations before beginning. On one cadaver(the same one from which the respiratory system and the heart were removed), we will totally remove the GI tract from the esophagus to the rectum (see below).

Begin with a midventral incision from the xiphoid process to the lateral edges of the rib cage. Two more lateral incisions are needed across the inguinal canals. These incisions should be verysuperficial to preserve the ductus deferens and the epigastric vein. Make a midline incision from the xyphoid process to the pubis.

Removal of part of the rib cage is necessary for viewing the liver and its underlying structures completely. The small bone cutter seems to work best in this case; feel free to cut or break ribs as necessary. NOTE: The rib cage may have been removed in previous dissection. Also, the abdomen may have been previously dissected, in which case the muscles simply need to be cut as necessary to expose the internal organs.

To expose the stomach and pancreas, cut the lesser omentum located on the lesser curvature of the stomach. Take care not to damage any large blood vessels in the area. DO NOT remove the greater omentum, but pull it to one side. The so-called cardia is located at the junction of the esophagus and stomach. Although there is no actual sphincter, smooth muscle in the esophagus serves that function. The fundus is the "hump" on the superior aspect of the stomach. Follow the pylorus of the stomach to the pyloric sphincter.

The first part of the small intestine is the duodenum. It is 10-12 inches long and curves medially before becoming the jejunum. Follow the jejunum to where it becomes the ileum. NOTE: The jejunum may be distinguished from the ileum by the thickness of the jejunal wall compared to that of the ileum. DO NOT cut the mesenteries because there are important blood vessels in them that are easily torn. Follow the ileum to the ileocecal valve. Off the cecum, you should find the vermiform appendix, if one is still present.

Follow the ascending colon upward from the cecum. It may have to be detached from the greater omentum. Find the transverse colon, which lies horizontally across to the descending colon and will lead to the "S"-shaped sigmoid colon. Be careful when removing connective tissue near the sigmoid colon because the testicular/ovarian vessels run through it in the pelvic region.

Locate the gallbladder on the underside of the liver. A significant amount of fat and connective tissue may have to be removed to expose these properly. The cystic ductcomes off the gallbladder and joins the common hepatic duct (formed by the hepatic ducts) to form the common bile duct, which leads to the duodenum. The entrance into the duodenum is through the hepatopancreatic ampulla, which is guarded by the sphincter of Oddi. The pancreatic ductmay be located where it joins the common bile duct before entering the duodenum. Trace the pancreatic duct back to the pancreas.

Locate the spleen in the upper left quadrant. Clean away fat and connective tissue but DO NOT destroy any vessels.

Ducts may best be isolated by opening the duodenum, probing the ducts and removing connective tissue.

SALIVARY GLANDS: (See Netter, p. 55).

The glands are whitish or cream colored and have a very different texture than either the fat or the muscle around them.

THE PAROTID GLAND:
Make an incision from the level of the ear and follow the angle of the jaw to the chin. Make another incision from the ear extending medially to the cheekbone. Carefully clear away fat and connective tissue to expose the parotid gland, which lies on the masseter muscle. Care must be taken when exposing the parotid duct (Stenson's duct), which lies within this connective tissue.

THE SUBMANDIBULAR AND SUBLINGUAL GLANDS:

Follow the cut along the angle of the jaw under the chin and along the opposite jawline. Peel the skin back to expose the underside of the chin. The submandibular gland is under the mandible close to the angle of the jaw. The sublingual gland is directly above the submandibular gland. You should be able to locate the Wharton's duct (the ducts of Rivinus) but don't worry about the duct of the sublingual gland.

STRUCTURES TO BE LABELED:
In addition to the structures in bold, label the following:

Visceral Peritoneum

Lesser Omentum

Mesentery

REMOVAL OF THE GI TRACT FROM ONE CADAVER:

Free the esophagus from its attachment with the diaphragm and use blunt dissection to free all mesenteries attached to the internal abdominal wall. Locate the abdominal arteries, viens and bile duct, and cut them close to the GI organ, leaving most of their length attached to the aorta or vena cava. If necessary, remove the greater omentum. Sever the sigmoid colon about where it becomes the rectum, remove visible waste and sew up the ends. Remove the entire tract and place it in a large bucket with wet cheesecloth. Label as indicated.

DISSECTION OF THE PERIPHERAL NERVES

The skin incision has been made from a previous dissection. Begin by exposing the brachial plexus. Using the subclavian artery as a landmark, clean the area using a blunt probe, locating the roots of the plexus. At the level of the axillary artery, find the three cords. Intertwined around the area where the axillary becomes the brachial artery, this plexus can be found. The lateral cord should be located and followed to the branching of the musculocutaneous nerve, which dives into the coracobrachialis, and median nerve. The medial nerve arises from both the lateral and medial cords. It should be followed distally on the medial aspect of the arm. The axillary and radial nerve branch from the posterior cord. Follow the radial nerve distally as it runs along the humerus, crossing from the medial to lateral aspect as it crosses toward the elbow. It runs down the lateral aspect of the arm to the wrist. Find the ulnar nerve behind the median epicondyle of the humerus and follow it anteriorly to the medial cord, then posteriorly along the anterior aspect of the ulna.

STRUCTURES TO BE LABELED:

Brachial Plexus

Lateral Cord

Musculocutaneous n.

Medial Cord

Median n.

Ulnar n.

Posterior Cord

Axillary n.

Radial n.

ANTERIOR LEG NERVES AND ABDOMINAL NERVES: (See Netter, pp. 506-510.)

The skin incision was made from a previous dissection. The only nerve on the front of the leg is the femoral. This can be located at the inguinal region next to the femoral artery and vein.

Three nerves are located in the abdomen and will be found during the dissection of the GI tract. The first is the obturator nerve, which runs deep to the perineal area and lies along the medial aspect of the psoas major. The second is the femoral nerve, which passes through the inguinal canal and lies next to the femoral artery and vein. The third is the lateral femoral cutaneous nerve, which runs through the connective tissue covering of the iliacus, and passes through the inguinal canal to the leg.

STRUCTURES TO BE LABELED:

Lumbar Plexus Lateral Femoral Cutaneous n.

Obturator n.

Femoral n.

POSTERIOR LEG NERVES:

The skin incision was done during a previous dissection. The buttocks nerves are to be done only on the cadaver with the deep leg muscle dissection. Locate the superior and inferior gluteal nerves on either side of the piriformis with the arteries. The pudendal nerve runs deep in the perineal area along the medial aspect of the gluteus maximus. The posterior femoral cutaneous is a small nerve running parallel to the sciatic in the upper buttocks.

The remainder of the posterior leg muscles should be done on both superficial and deep muscle cadavers. The sciatic is the large nerve located in the upper thigh. The sciatic branches into the common peroneal and the tibial nerves. The peroneal runs to the lateral aspect of the leg where it branches above the fibula into the superficial and deep peroneals. The tibial runs down the center of the leg for a short distance and then runs toward the medial aspect of the leg to the ankle.

STRUCTURES TO BE LABELED:

Sacral Plexus

Gluteal Region

Superior Gluteal n.

Inferior Gluteal n.

Pudendal n.

Posterior Cutaneous n.

Posterior Thigh Region

Sciatic n.

Tibial n.

Common Peroneal n.

Peroneal Region (lower leg)

Superficial Peroneal n.

Deep Peroneal n.

DISSECTION OF THE BLOOD VESSELS OF THE ABDOMEN AND URINARY TRACT

The abdominal blood vessels are embedded in connective tissue and can be very fragile. Extreme carein locating and identifying them is necessary. There is no set routine as to which vessels should be done first, so begin with arteries from the cranial or caudal areas of the aorta. Label all structures shown in small caps.

The first branch off the aorta is the celiac trunk. This is a very short vessel that gives rise to three branches: 1) the left gastric that runs to the left and follows the lesser curvature of the stomach, 2) the splenic that runs to the left to the spleen (occasionally embedded in the pancreas), 3) the common hepatic that runs to the right. The common hepatic branches into the 1) gastroduodenal, which runs under the duodenum and then curves to the left following the greater curvature of the stomach; 2) the right gastric, which runs posteriorly and then curves to the left following the lesser curvature until it anastomoses with the left gastric. (NOTE: There is variability as to where this artery derives. Several possibilities exist, such as the right gastric could come off the common hepatic artery, the gastroduodenal artery or the hepatic artery. When attempting to locate this artery, keep in mind that at some point it must be going posteriorly toward the lesser curvature of the stomach.); and 3) the hepatic that runs to the liver.

The next branch off the aorta is the superior mesenteric artery. This runs posteriorly before entering the mesenteries of the small bowel. NOTE: These arteries are difficult to find. Since the cadavers we use are elderly, these arteries have probably atrophied. Consequently, they are thread-like and thus easily missed when dissecting.

Below the superior mesenteric on either side of the aorta, the renal arteries lead to the kidneys. Suprarenal arteries are minuscule and arise from the aorta and the renal arteries.

Below the renals, on the ventral side of the aorta, are the ovarian/testicular arteries. These are in a connective tissue sheath that eventually runs through the parietal peritoneum to the pelvis.

The inferior mesenteric artery arises from the aorta ventrally above where it branches into the common iliacs. Both the common iliac arteries branch into the superficial and deep iliac arteries.

Directly dorsal to the iliac arteries, the iliac veins branch in the same fashion. The common iliac veins run to the vena cava that is to the right of the aorta.

Anteriorly to the branches of the iliacs, the lumbar arteries and veins arise from the dorsal side of the aorta and vena cava. On the median side of the aorta and vena cava, the lumbars alternate in an overlapping fashion before encircling the vertebral column.

The ovarian/testicular veins are not symmetrical as are the arteries. On the right, it comes off the vena cava. On the left, it comes off the renal vein.

The renal veins are larger than the arteries and usually lie directly over the arteries. The left renal vein is longer and has a branch, the suprarenal vein, that leads to the adrenal gland.

The portal system is separate from the vena cava and the rest of the abdominal veins. It is best found by locating the spleen and the splenic artery. The splenic vein is large and usually runs with the artery. Once the splenic vein is located, follow it to the right. The first vessel that joins the splenic is the inferior mesenteric vein, which returns blood from the large intestine. The next large vessel that joins the inferior mesenteric and splenic veins is the superior mesenteric vein, which returns blood from the small bowel and runs in those mesenteries. The union of the superior mesenteric, inferior mesenteric and the splenic gives rise to the portal vein, which runs to the liver.

URINARY TRACT:

Once the renal vessels are found, the kidneys can be easily located retroperitoneal under a fat pad. On the left, remove the fat pad and peritoneum to expose the kidney and adrenal gland. The adrenal gland is loosely attached to the kidney and is embedded in fat. Use blunt technique to isolate the glandular tissue from the fat.

Carefully remove the left kidney and adrenal gland from one cadaver, cutting the ureter a few cm away from the hilus of the kidney. Make a sagittal section through the kidney to produce two symmetrical halves. Locate and tag the cortex, renal capsule, pyramid(s) major and minor calyces and renal pelvis.

Locate the ureter (on both sides) and remove it from the peritoneum all the way to the bladder. Make an "X" through the bladder on the anterior side (or cut a wedge) and remove a portion to expose the bladder's interior and the opening of the urethra and ureters.



FIGURES. 14.1 & 14.2 Abdominal Arteries and Veins

DISSECTION OF THE HUMAN BRAIN

(See Netter, pp. 94-109.)

SKIN INCISION:

Using a scalpel, make an incision in the median plane, down to the bone, from the eyebrows posteriorly to the base of the skull. Make a second incision from ear to ear. Reflect the skin back far enough to have a clear view of the entire cranium. The skin reflects very easily and should be peeled back as far as possible both laterally and on the posterior of the skull.

NOTE: If the temporalis muscle is still attached, lift off the muscle and reflect it downward to the level of zygomatic arch. Scrape the bones clean. (Figure 15.1.)

FIGURE 15.1. REMOVING THE SKULL CAP:

Before using the bone saw, make a line about half an inch above the level of the supraorbital margins. If the cadaver you are working on is not the one that will be used for the eye dissection, this margin can be lower, which, in turn, will make the brain easier to retrieve. When you have reached the ears, however, angle the blade toward the bottom of the occipital lobe. This will make the retrieval of an intact cerebellum possible. Additionally, it will make the bone and medulla easier to retract. Care must be taken if the ear dissection is to follow.

CARE MUST BE TAKEN, ESPECIALLY IN THE TEMPORALIS REGIONS, WHERE THE BONE IS MUCH THINNER THAN EXPECTED.

Using the bone saw, make grooves in the skull at a shallow depth of approximately 1-2 millimeters, without completely penetrating the skull. Do this for the entire circumference of the skull, following the line that was drawn earlier. Now, starting at the anterior portion of the skull, place the chisel in the groove you have just cut and gently hammer through the skull. Do this circumferentially around the head in locations approximately 1-2 inches apart. Again, be careful in the temporalis regions. After several of these cuts have been made with the hammer and chisel, use the chisel to pry the skull cap off. Use a scalpel or metal spatula to sever connections of the dura mater with the skill, eventually wedging fingers in and running them underneath the skull cap. After the skull cap has been removed, use the bone saw to make an additional cut along each side of the occipital portion of the skull and pry the bone away laterally (see Fig. 15.3). This should produce a triangle that opens up the occipital bone, exposing the cerebellum and the brainstem connection with the spinal cord.

FIGURE 15.2. Using the bone saw.

FIGURE 15.3. BRAIN REMOVAL:

Carefully separate the dura mater, leaving most of it attached to the brain, if possible. Once the skull cap has been removed and the brain is exposed, it is very easy to forget about the cerebellum. Be careful that you do not get carried away breaking bone away from the brain and forget about the tentorium. It is a thin bone covering the cerebellum and must be removed with care before attempting to remove the brain. Carefully cut away the dura mater and other tissue to expose the connection of brainstem and spinal cord. If the spinal cord dissection has already been done, you will want to remove the brain and cord from one cadaver with the attachment intact. The brain can be slightly wiggled in its cavity and gently pulled out about half an inch. This will allow the prosector to look under the frontal lobe and see the cranial nerves. The most visible is the optic chiasma. The cranial nerves should be cut above the level of the chiasma, but not next to the brain. This will allow for the origin to be seen on the brain. As the brain is lifted slightly, a spatula can be used to sever the connection. It may be easiest and most effective to simply get your fingers down at the midbrain, have someone lift the brain, and break the connection by thrusting your fingers through it. The brain can now be gently wiggled out of the skull, paying heed to the separation of the brain from the dura mater. If it doesn't seem to be coming out easily, more than likely there is either dura mater or a cranial nerve that needs to be removed from the brain (Figure 15.4).

BRAIN DISSECTION:

On one of the brains, leave the brain in the skull and carefully cut the dura mater along the median plane by making a small fold with a pair of forceps, nicking it with the scalpel, and inserting a pair of scissors. Remove the dura mater from only one half of the brain; the other half will be kept intact. Using one of the larger knives, make an incision one inch from the midsagittal plane through the brain. By elevating the smaller hemisphere with your hand and releasing parts that are still connected with a scalpel, remove this half of the brain from the skull. (Figure 15.4.)

FIGURE 15.4. 

STRUCTURES TO BE LABELED:

Cerebellum

Cerebral Peduncles

Choroid Plexus

Corpora Quadrigemina

Corpus Callosum

Dura Mater

Fornix

Fourth Ventricle

Frontal Lobe

Hypothalamus

Infundibulum

Intermediate Mass

Medulla Oblongata

Occipital Lobe

Optic Chiasma

Parietal Lobe

Pineal Body

Pituitary

Pons

Septum Pellucidum

Temporal Lobe

Thalamus

Third Ventricle

ALTERNATE DISSECTION OF THE HUMAN BRAIN:

Removal of Skull Cap:

1) Make a groove with the bone saw approximately 10 millimeters above the level of the supraorbital margins across the anterior aspect of the skull. (See Figure 15.5.)

2) The groove should continue across the lateral aspect of the skull and intersect the point of fusion of the sphenoid bone, parietal bone and temporal bone (temporal fossa and pterion). (See Figure 15.6.)

3) The groove should now be angled downward toward the point of intersection of the parietal bone, mastoid process of temporal bone and occipital bone (lambdoid suture). (See Figure 15.6.)

4) The groove should continue at an angle toward the lateral aspect of foramen magnum, passing medially to the condylar foramen and fossa. (See Figure 15.7--top.)

5) Using the bone saw, make a groove on the frontal bone intersecting the first groove above the supraorbital margin, and extending anterior to posterior and intersecting and continuous with the sagittal suture. (See Figures 15.5, 15.7--bottom.)

6) The groove should continue along the sagittal suture and intersect the lambda/lambdoid suture. From this point, the groove should continue along the posterior aspect of the skull on a med-sagittal plane, dividing the occipital bone. This mid-sagittal groove should continue to the foramen magnum. (See Figure 15.7.)

7) Starting with the mid-sagittal groove, the groove can be separated by inserting a chisel and twisting. This procedure should be continued around the circumference of the skull.

NOTE: Grooves should be cut to a depth of approximately 3-4 millimeters, or until a moist fluid appears in the groove.

8) This procedure should result in the bones of the skull separating easily, resulting in a brain that is extremely easy to remove.

FIGURE 15.5.

FIGURE 15.6.

FIGURE 15.7.

DISSECTION OF THE ENDOCRINE GLANDS

In order to expose the pancreas and adrenal (suprarenal) glands, the abdomen must be opened if it has not already been done in an earlier dissection. Directions for opening the abdomen are contained in the first two paragraphs of the chapter on gastrointestinal dissections.

Pancreas:

The pancreas is located in the abdomen just posterior to the stomach. The head of the pancreas lies in the curve of the duodenum and the tail touches the spleen. The lesser omentum, which stretches between the lesser curvature of the stomach and the liver, may have to be partially removed in order to get underneath the stomach. The pancreas is a relatively fragile organ so take care not to tear it when removing surrounding adipose tissue. Avoid cutting the splenic vein and artery, which run along its upper posterior border.

Adrenal (suprarenal) glands:

The adrenal glands are most easily found by first locating the kidneys, which lie behind the parietal peritoneum in the posterior abdominal wall. The superior pole of each kidney lies at the level of the 11th or 12th rib. The adrenal glands lie within the renal fat on the superior and medial aspects of each kidney. It may be difficult to distinguish between fat and gland. If you are having trouble locating the adrenal gland, follow the adrenal (suprarenal) vein as it comes off the renal vein on the left side of the cadaver. The adrenal glands do not adhere to the kidneys, although some pictures make it appear so.

NECK: (See Netter, pp. 68-70.)

Partial exposure of the thyroid and parathyroid glandsare accomplished with the respiratory dissection and, to a lesser degree, with the dissection of the heart and blood vessels of the head and neck.

Thyroid:

If the respiratory dissection has not yet been done and only the blood vessels of the head, neck and heart have been dissected, the "strap" muscles of the neck will need to be reflected and/or removed. These muscles, the sternohyoids and omohyoids, form the most superficial and medial aspect; the deeper, more coronal thyrohyoids and the sternothyroids are below them. The most superficial of all the neck muscles, the sternocleidomastoids, have probably already been removed along with the omohyoids.

The thyroids consists of two conical lobes connected by a broad isthmus. It extends from the lower third of the thyroid and cricoid cartilages. Using these as landmarks and palpating the region for a lateral moving mass will help you locate the thyroid.

The thyroid and parathyroid glands are encased in a fine, fibrous capsule derived from fascia in front of the trachea (retracheal fascial). This and the thyroid gland are found in front of the trachea, right above the manubrium of the sternum. One thyroid lobe is at the right side of the trachea, and one to the left, with both connected medially by the isthmus.

NOTE: TAKE CARE WHEN DISSECTING AWAY BLOOD VESSELS, MUSCULATURE, AND THIS FINE CAPSULE. Only blunt probes, non-rat-toothed forceps and scissors should be used. Scissors should be used primarily as a separation tool, going from a closed to open position to separate tissues. Tissues should only be cut after separated in this manner. This technique will ensure that the small parathyroids are not pulled out or cut away.

Parathyroids:

Usually two of these tiny glands are found on each lobe of the larger thyroid. They will be at the junction of the posterior-anterior surfaces at the uppermost end and approximately mid-way approaching the isthmus. Careful dissection, as described above, of the thyroid away from the trachea at the dorsal border will allow some reflection so that the posterior-anterior junction can be viewed. Vasculature may be left intact until the parathyroids are located. The parathyroids will appear as tiny vesicle-like structures of a darker, more translucent tissue. They may be purplish-red in hue.

NOTE: Some reference books describe them as yellowish-brown, 3-8 mm in length, 2-5 mm wide and 1.5 mm deep. The lack of the actual photos of the parathyroid glands make identification difficult.

The pituitary gland will be exposed during the brain dissection so you are not responsible for it here. The thymus gland, lying over the pericardial sac, is usually only found in children. By adulthood it has atrophied to the extent that it is no longer distinguishable from the surrounding connective tissue. You are also not responsible for this organ.

STRUCTURES TO BE LABELED:

Pancreas

Adrenal

Thyroid

Parathyroids

Thymus

Pituitary

DISSECTION OF THE CRANIAL NERVES

Use the alternate method for skin incision and skull removal (p. 60). Use the bone saw deeply (3-4 mm) so that the dura is also cut. A complete cut through bone and dura will allow the bone to lift off more easily.

REMOVAL OF THE BRAIN:

With the large knife, slice off the top section of the brain. You may want to slice several ½" to 1" sections to observe interior structures. Cranial nerves are fairly deep so you will not damage them. Once the brain has been cut to the level of the bone, begin slicing small sections of the frontal lobes until you are able to see the olfactories resting on the cribriform plate. From that point on, move towards the back with care. Do not try to lift the frontal lobes as this will tear the fragile olfactories from the cribriform plate. If by accident they are removed, save them and lay them back in the groove they came from. The brain should be removed in chunks from the lateral aspects of the skull. Most of the nerves are located in the center one-third of the skull.

DISSECTION OF THE NERVES:

Carefully pick the brain tissue from around the nerves, leaving the nerves as long as possible. Start with the first nerve (olfactory) and work posteriorly to the foramen magnum, where V through XXII will be found. Remove the dura from the bones remaining. If possible, do not disturb the nerves as they pass through the various foramina. (See Netter, pp. 98, 108-113.)

The trochlear (IV) and abducens (VI) are particularly small and fragile. Both emerge with the trigeminal nerve. Identify all three parts of the trigeminal nerve.

IDENTIFY the following structures, but do not label them due to their fragile nature.

Olfactory nerve (I)

Olfactory bulb

Olfactory tract

Optic nerve (II)

Optic chiasma

Optic tract

Oculomotor nerve (III)

Trochlear nerve (IV) Trigeminal nerve (V)

Mandibular

Maxillary

Ophthalmic

Abducens (VI)

Facial nerve (VII)

Statoacoustic (Vestibulocochlear) nerve (VIII)

Vestibular nerve

Cochlear nerve

Glossopharyngeal nerve (IX)

Vagus nerve (X)

Accessory nerve (XI)

Hypoglossal nerve (XII)

Cribriform plate

Optic foramen

Superior Orbital Fissure

Foramen Rotundum

Foramen Ovale

Internal Acoustic Meatus

Jugular Foramen

Hypoglossal Canal

DISSECTION OF THE MALE REPRODUCTIVE TRACT

(See Netter, pp. 358-363.)

EXTERNAL:

Skin incision:

From one side, start at the medial edge of the upper leg incision and make two cuts: one down the middle on the lateral side of the scrotum, the other down the middle on the anterior side of the scrotum, making a wedge-shaped skin flap, leaving the skin attached at the distal aspect of the scrotum. This incision allows you to reflect the skin from the proximal aspect distally. Make sure your wedge is wide enough to expose one testis. (Figure 18.1.) (See Netter, p. 365.) (Occasionally, a cadaver has only one testis; check this out before relying on having a second one.)

Reflect the skin:

Clean the inguinal area to show how the spermatic cord ends at the inguinal canal and the ductus deferens enters the abdomen. Look for inguinal nodes if not already noted.

Scrotum:

On one side (the side of the unexposed testis) leave the spermatic cord intact, gently removing the connective tissue covering to expose the cremaster muscle. This muscle is composed of thin, longitudinal fibers that seem meshed in the connective tissue.

On the other side, expose the blood vessels, vas deferens (ductus deferens)and epididymis by opening the spermatic cord. Slit the white (or pink), shiny tunica vaginalis, exposing the testis. Cut longitudinally through the testis to the rete testis to be spread open and observe the clear-to-white tunica albuginea and seminiferous tubules.

Penis:

At the tip of the penis, find the opening of the urethra and make a careful incision following the urethra on the ventral side back to the root of the penis. Gently spread apart the two halves of the penis and continue the incision deep until the penis is completely bisected. (Figure 18.2.)

INTERNAL:

Follow the spermatic cord through the inguinal canal into the abdomen. Follow it as it descends retroperitoneal into the perineum along the body wall. Near this junction look for the ductus deferensand dissect this structure. You will not be able to show the prostate from this view as it is very deep beneath the bladder.

LABEL:

Vas Deferens glans penis

Epididymis prepuce

Tunica Vaginalis penile urethra

Tunica Albuginea spermatic cord

Corpora Cavernosa cremaster muscle

Corpus Spongiosum

PRONE DISSECTION:

NOTE: Use a cadaver in which the skin and gluteal muscles have already been cut and reflected back.

Exposing the Prostate:

NOTE: You may wish to remove a portion of the sacrum to make the following dissection easier.

Remove adipose tissue to expose the rectum. Make a transverse cut of the rectum at about its junction with the sigmoid colon. Beyond (anterior to) the rectum, you should find the prostatealong with the seminal vesicles, ductus deferens, prostatic urethra, ejaculatory duct and the membranous urethra. Be careful and you should find the bulbourethral glands while removing the surrounding structures. They are about two inches distal to the prostate gland. At this point, it is very difficult to see them; their color is the same as the surrounding tissues. They are composed of spongy, glandular tissue contained by a smooth membrane which helps to distinguish them. Also attempt to preserve the bulbosponglosus muscle at the base of the penis.

NOTE: Once you have cut the rectum, tie both ends and remove any feces that may have leaked. The posterior surfaces of the prostate gland, seminal vesicles and membranous urethra are all in contact with the anterior wall of the rectum. This is why you must proceed slowly and carefully with this part of the procedure.

While removing the rectum and clearing the adjacent tissue, take special precautions to expose the tiny, pea-shaped bulbourethral glands, which lie just superficial to the membranous urethra and inferior to the prostate gland itself. These glands are difficult to differentiate from surrounding tissue and may have atrophied in the elderly male.

After removing the anterior wall of the rectum, carefully remove as much tissue as you can surrounding the sides of the prostate gland, the posterior surface and sides of the membranous urethra and the posterior surface of the right and left seminal vesicles, making all of these clearly visible with clearly defined borders. Note that the prostate gland is a very tough tissue and does not feel spongy with the scalpel. However, if you cut into it, you can see that it is spongy in appearance.

Using the scalpel, slowly and carefully make a sagittal incision down the center of the prostate gland only to a depth of the prostatic urethra. Once you've identified the correct depth, cut a small wedge out of the prostate, using your initial cut as a guide, so that the interior of the gland, including the prostatic urethra, is clearly visible.

LABEL:

Right and Left Seminal Vesicles

Prostatic Urethra

Prostate Gland

Membranous Urethra

DISSECTION OF THE FEMALE REPRODUCTIVE TRACT

(See Netter, pp. 348-357.)

The abdominal incision was made during a previous dissection.

NOTE: Take great care when dissecting out the suspensory ligament, which contains the ovarian artery and vein--they can be very easily cut!

Exposure of the Abdominal Organs:

The top of the uterus should be visible in the lower abdominal cavity. The broad ligament extends laterally on either side of the uterus from top to bottom of the uterus. At the top of the uterus, the fallopian tubes extend laterally and are enclosed in the broad ligament. Running along side the fallopian tube is the ovarian ligament. From the anterior side of the ovary, running anterior in the abdominal cavity, is the suspensory ligament. This encloses the ovarian vein and artery. The last ligament enclosed in the broad ligament is the round ligament. The round ligament arises below the fallopian tube on either side of the uterus. The round ligament runs ventrally to the anterior abdominal wall.

On one side of the uterus, trim the broad ligament from around the round ligament, the ovarian ligament and the fallopian tube. Leave the other side intact. On the ventral side of the uterus, make a slit down to the endometrial lining. If necessary, cut a triangular or circular "window" in order to see the layers of the uterine wall.

Exposure of the External Genitalia:

Not much needs to be done in this area. Make a slit in the prepuce of the clitoris to expose the clitoral stalk.

Exposure of the Breast:

Make a wedge-shaped cut through the nipple through the fat to the connective tissue on top of the pectoralis major. Remove some of the fat to expose the ducts and sinuses. The glandular tissue is a whiter color than the fat surrounding the glands.

LABEL:

Broad ligament

Round ligament

Uterine (Fallopian) tube

Fimbriae

Suspensory ligament

Ovarian vein and artery (if not already labeled from Abdominal Vessels lab)

Ovarian ligament

DISSECTION OF EYE

(See Netter, pp. 76-86.)

Place the cadaver in a prone position with the head raised slightly. To expose the eye for easy accessibility, it is necessary to remove the superior portion of the skull with complete transverse section, removing at least the anterior portion of the crown. The transverse cut (with autopsy saw) should be lightly superior to the ridge of the supraorbital margin of the frontal bone. With the floor of the cranium exposed, make two vertical incisions carefully with the bone saw through the frontal bone: one through the supraorbital foramen, down to the upper margin of the sphenoid bone; a second lateral to the orbit, down through the frontal bone. Then cut so as to join these two cuts with a cut along the joint of the sphenoid and the frontal bones. Carefully remove this wedge of bone, using scalpel and scissors to gently cut through the orbital facia exposing the eye and muscles. Be careful with the depth of the mid-line incision because of the trochlea. (Figure 20.1.)

Carefully clean away the postorbital fat pad to expose the extrinsic muscles of the eye. Once the postorbital fat pad has been removed, locate the lateral rectus, inferior rectus and inferior oblique muscles. With the location of these muscles in mind, cut and remove the portion of the zygomatic bone that makes up the lateral orbit. The removal of this section of bone gives the prosector plenty of room to remove the tissue surrounding the extrinsic muscles and optic nerve, and also gives the students a better view of the muscles. Do not cut the levator palpebrae superioris muscle unless exposure of the superior or inferior rectus muscles is impossible. Careful removal of the fat should allow location of all the muscles without cutting the levator muscle. The inferior oblique is difficult to expose, and the superior rectus and levatator palbebraesuperioris muscle may need to be cut.

STRUCTURES TO BE LABELED:

Levator Palpebrae Superioris Superior Rectus

Superior Oblique Inferior Rectus

Inferior Oblique Medial and Lateral Rectus

Trochlea

It may be helpful to dissect one orbit anteriorly, removing the skin and surface tissues to bone in area around the orbit, exposing the lacrimal gland, trochlea and rectus muscles. To expose the lacrimal duct, make a very superficial incision on the face from the corner of the eye medially toward the nose, then inferiorly along the side of the nose. Reflect the skin carefully as the duct is superficial and difficult to discern from the skin. Expose the nasolacrimal duct along the nose. It may be helpful to inject water through the lacrimal puncta to slightly expand the duct.

STRUCTURES TO BE LOCATED: Lacrimal duct, puncta, caruncle, nasolacrimal duct, lacrimal gland.

NOTE: Find the lacrimal gland behind the lateral side of the eyelid. (See the prosector's copy of the Color Atlas of Anatomy on page 123.)

OPTIONAL REMOVAL OF ONE EYE:

If materials and time permit, one eye may be entirely excised, either anteriorly or from the cranium, and its muscles, etc., labeled. Carefully cut each structure as far from the eye as possible.

FIGURE 20.1.

DISSECTION OF THE EAR

(See Netter, pp. 87-93.)

The top of the skull and half of the brain were removed during a previous dissection.

EXTERNAL:

Step 1. On the outside of the head continue to peel the scalp away from the skull, cutting through the external acoustical meatus from under the scalp (Figure 21.2), pulling the skin far enough away so you can see into the external meatus. Carefully clean the meatus of wax. It is very deep, but don't damage the tympanic membrane.

Step 2. With the bone saw, cut through the temporal bone on either side above the meatus, then across the top of the meatus (Figure 21.3), and remove the square of bone.

Step 3. Slice away pieces of bone from above the meatus (where the lines are in Figure 21.2) until you can easily see the tympanic membrane. Don't try to remove very much or you may damage the membrane. Shining a light through the floor of the cranium might help to locate the tympanic membrane. Once it is readily visible, stop.

INTERNAL:

Looking into the floor of the cranium, locate the ridge of bone that is over the inner ear (Figure 21.1). By shining a light into the external ear, you may be able to see the cavity in which the middle ear bones lie (Figure 21.2).

Step 4. Using a pointed probe and mallet, carefully chip through the bone just medial to the spot you think is directly above the ear drum (indicated by an arrow in Figure 21.2). Try not to break all the way through or you will disturb the middle ear bones. Once you make a crack, use bone-cutting pliers to peal up the bone. Expose the malleus, incus and tympanic membrane. It is almost impossible to expose the stapes at the same time without destroying the other two, so don't try. Don't worry about labeling anything; they are too fragile.

Step 5. Use the plastic ear model and the manuals to get an idea of where the parts of the inner ear are located. Then, carefully chip away at the bone until you can make out the structures (semicircular canals, cochlea, and vestibule). It's rather tricky because you will be removing bone from bone, but don't worry when you start as you'll get a feel for what you are doing.

FIGURES 21.1, 21,2 & 21.3.