Appendix A Dissection Instructions for a Goat Cadaver
A.1 Dissection Labs
The time frame for dissection of a goat cadaver will be determined by your instructor based on your course contents and schedule. The dissection plan described requires a minimum of nine labs. The head can be demoed as a stand‐alone lab. The bovine and caprine heads are compared for musculoskeletal structures, blood vessels, and nerves (watch Videos 4, 5, and 6).
Suggested setup for the head lab is as follows: midsagittal and lateral views of the bovine and caprine heads could be discussed on one side of the lab while teeth (aging), horn structures, and paranasal sinuses could be discussed on the other side. Specimen/station numbers needed for this lab depend on the student numbers.
When dissecting the limbs, the first lab covers the musculoskeletal system while the second lab covers the blood vessels and nerves. Dissection of the neck and body cavities (thorax, abdomen, and pelvis) are completed as one unit in four sequential labs. Organs and structures in the thorax, abdomen, and pelvis should be studied first in situ (for topography) and later as isolated viscera (for a more detailed study of the heart, abdominal viscera, and isolated male and female reproductive tracts).
A.2 Dissection of Goat Neck and Body Cavities (Labs, 1, 2, and 3)
Each group of six students should have one goat or sheep. From here on, we refer to the goat, but the sheep is very similar. We would like the even numbered groups to open the right side of the animal and the odd numbered groups to open the left side.
You may use a large knife for some of the skinning, but we suggest using no. 20 or 22 scalpel blades and handle no. 4 for most of the dissection (see Video 24).
It is very important for you to follow each step of these directions and see all the structures listed on your lab ID before moving on. We move quickly through the ruminant anatomy so get as much as you can out of each lab.
A.2.1 Removal of the Thoracic Limb
Lay the goat on its side on the table and have someone pull the thoracic limb you will be removing away from the body.
Using a sharp knife or scalpel, cut through the skin and muscles just behind the thoracic limb. You will feel the blade against the ribs when you are deep enough.
Extend the cut behind the thoracic limb from the dorsal midline down close to the sternum.
Turn the blade so that it lies flat against the body wall and cut the deep and superficial pectorals from caudal to cranial as close to the sternum as possible (Figure A.1).
When you reach the level of the thoracic inlet, turn the blade and cut dorsally in front of the limb.
Return to your ventral cut and sever any remaining brachial plexus or axillary blood vessels on the medial side of the limb. Finally, cut through the attachments of the serratus ventralis muscle on the deep surface of the scapula and the remaining rhomboideus muscle attachment at the dorsal border of the scapula. Now you will be able to remove the thoracic limb.
The instructor will provide you with a plastic bag to place the limb for further dissection later.
A.2.2 Removal of the Pelvic (Hind) Limb
Have someone elevate the pelvic limb that is to be removed to allow the dissector good access to the inguinal area with his or her blade (Figure A.1). A knife would be the best tool to use here.
The purpose of the first cut is to sever the adductor muscles where they attach to the pelvic symphysis. Incise the skin between the legs just lateral to the midline on the side you will be removing (Figure A.1).
If you have a male, be careful not to cut the penis. The penis should remain with the pelvis when the limb is removed.
Make a deep cut dorsally through the adductor muscles with the person elevating the limb lifting as the cut is made to open the space between the limb and the pelvis.
If the initial cut is made correctly, you should feel the knife hit the bottom of the pelvis or possibly the acetabulum (review this area on a skeleton). Use your blade tip to find the bottom of the hip joint and cut into it. When you find the joint, you will probably see synovial fluid. Also, as you cut the ligament of the head of the femur, you will find the leg much easier to elevate.
At this point, the hard work is done. Cut the lateral thigh muscles from the pelvis, leaving some muscles covering the sacrosciatic ligament.
Once the hind limb is free, put it in the plastic bag with the thoracic limb or in a separate bag for later dissection.
A.2.3 Skinning of the Neck and Flank on the Side Where the Limbs Are Removed
Now it is time to skin your specimen. Because of the rapid pace, we will be moving at, we are going to skin the entire left/right side.
Make a skin incision just behind the ear from the dorsal midline to the ventral surface of the neck (Figure A.1).
Make another skin incision along the ventral midline connecting your first cut on the ventral neck and extending all the way back to the inguinal area. There will be big holes in your skin where the thoracic and hind limbs used to be.
As you continue the skin incision back toward the inguinal area, cut lateral to the penis if you have a male or lateral to the udder if you have a female.
Join the ventral incision in the inguinal region with the cut you made to remove the pelvic limb (Figure A.1).
Now you should remove the skin, folding it dorsally and exposing the neck, thorax, and abdomen. Do not worry about the cutaneus trunci that should remain with the skin.
Reflect the skin to just a little beyond the dorsal midline, and leave it attached to the body. The skin will help hold in moisture when you put the cadaver away. Now it is time to see some anatomy!
Clean the superficial neck fascia. The external jugular vein lies in the jugular groove. Identify the muscular boundaries for the jugular groove. In the goat, the jugular groove is bounded by the sternomandibularis (sternozygomaticus) muscle ventrally, and the cleidomastoideus muscle (distal part of the brachiocephalicus muscle) dorsally.
The sternomandibularis muscle is commonly referred to as the sternozygomaticus muscle in the goat as it attaches to the zygomatic arch (see Figure 1.20 in Chapter 1).
The sternomandibularis muscle is absent in the sheep, making the jugular groove less distinct in this species.
You should see another muscle lying deep to the external jugular vein in the cranial part of the neck. This muscle is the sternomastoideus. Find the sternomastoideus muscle where it divides from the sternomandibularis muscle in the middle of the neck. The sternomandibularis and sternomastoideus form the sternocephalicus muscle.
Cut the sternomastoideus muscle just beyond its origin and reflect it dorsally to reveal the carotid sheath. By now, you should know what is in the carotid sheath. Identify its main contents (the common carotid artery and vagosympathetic nerve trunk) and move on.
A.2.4 Opening the Thorax and Abdomen for Studying the Topography on the Left and Right Sides
Now you are ready to open the thorax and abdomen. Remember we said we were moving fast! (See Video 10 if you have not already done so.)
Identify the following nerves on the thoracic wall:
Long thoracic nerve (see Figure 2.7 in Chapter 2). This is a motor nerve that supplies the serratus ventralis muscle.
Intercostal nerves, arteries, and veins. The intercostal vessels and nerves follow the caudal border of the ribs. You may see them better from the interior of the ribs when you reflect the rib cage dorsally. See Box A.1 for clinical relevance.