Notes on Dissections

The dissector used, Grants Dissector, 11th edition, is an excellent guide to the enterprise of human dissection that is the overall goal of this course. It generally provides a good introduction to each dissection and instructions for how to proceed. However, in some areas, this guidance does not conform as well to our particular anatomy course. In some cases this is because it includes areas we chose not to dissect or because the order in which we dissect certain regions differs from the order presented in the dissector, and in other instances, our experiences in the dissecting room have lead us to formulate different strategies than presented in the dissector. For all of these reasons, we include the following notes on dissection. They should be used as a supplement to the dissector, except as noted. We hope that these notes will help make your time spent in the dissection laboratory more valuable.

DISSECTION 1. Vertebral Column and Spinal Cord

Prepare for the lab by becoming thoroughly familiar with the bony anatomy of the region, particularly the composition of the vertebral column, and its relationship to the spinal cord and spinal nerves. The dissector (pp. 115-117) provides a pretty good review, but you may need more background. We also encourage you to use A.D.A.M. in the library. Figure 4.6 is not from The Late Show.

Follow the basic plan for dissection outlined in the dissector, but you do not need to attempt to locate the greater occipital nerve and occipital artery (p. 110).

Do attempt to identify a dorsal primary ramus of at least one spinal nerve.

Do attempt to dissect the erector spinae and transversospinalis groups of muscles.

Realize that various components of the transversospinal muscle group are optimally displayed at different vertebral levels.

You need only expose the spinal cord for 2 or 3 vertebral levels. We suggest that you work around T10-T12. In doing your dissection, DO NOT remove all the dorsal musculature from T6-L5, otherwise you will have nothing left to demonstrate. Remove only what you need to uncover the vertebrae at the desired levels. Do not use a saw to enter the vertebral canal. Use rib cutters, bone pliers, rongeurs, or a chisel.

Do not dissect the suboccipital region (pp. 123-125).

DISSECTIONS 2. Shoulder Region and Axilla

Begin by reviewing the bony anatomy of the shoulder region (Text or use A.D.A.M.) The dissector (pp. 161-162) will not provide sufficient background for this endeavor.

You do not need to skin the entire upper limb! Skin only as far distal as the elbow, the hand dissectors will want to do the rest. Be sure to preserve the superficial veins: cephalic, basilic, median cubital, and the cutaneous nerves (p. 160).

Review the mammary gland (p. 164), but it is not likely that your cadaver will have enough breast tissue to dissect.

Knowing the boundaries of the axilla is both helpful and important. Spend some time learning them before identifying them on your cadaver (p. 165).

DISSECTION 3. Gluteal Region, Thigh and Knee Joint

Begin by reviewing the bony anatomy of the region. Use your text (pp. 365-406), A.D.A.M., or a special A.D.A.M. module (The Gluteal Region). The review in the dissector (pp. 131 & 135) will not be enough.

You do not need to skin the entire lower limb. You may stop just below the knee. However, be careful to preserve the great saphenous vein and the cutaneous nerves of the thigh. Leave the small saphenous vein and small nerve and the origin of the great saphenous vein and digital branches of the superficial peroneal nerve for the team dissecting the leg and foot.

You should be able to find some inguinal lymph nodes but all of the groups may not be present.

Since you have not yet dissected the pelvis, you will not be able to study the continuity of the structures described on p. 138. Don't despair, you will do this later (Dissection 15).

Carefully coordinate your dissection of the knee joint (pp. 153-154) with your table mates working on the leg and foot.

DISSECTION 4. Forearm and Hand

Begin by studying the bony anatomy of the forearm and hand. You can use your text and/or A.D.A.M. The review on pp. 171 & 174 will be a good summary, but you will probably want more detail.

You will need to finish skinning of the forearm and hand. Please be careful to preserve superficial veins and cutaneous nerves.

DISSECTION 5. Leg and Foot

Begin by studying the bony anatomy of the leg and foot. You can use your text and/or A.D.A.M. or a special A.D.A.M. module called The Foot. The review in the dissector will be useful, but you will probably want more detail.

You will need to finish removing the skin and superficial fascia of the leg and foot. Please be careful to preserve the superficial veins and cutaneous nerves. Of special interest are the small saphenous vein and sural nerve on the posterior calf (p. 128) and the tributaries of the great saphenous vein and the superficial peroneal nerve (p. 129).

DISSECTION 6. Face and Cranial Contests

Prepare for this dissection by reviewing your skull, especially the foramina of the skull. Use the text. The A.D.A.M. module on this area is quite good. The dissector (pp. 185-186) is a good summary but you really need to know your way around before you begin to dissect.

Unless you have unlimited time, do not go overboard on the facial muscles. Many are so small that they are nothing at all but others are large and quite dissectable. Focus on those muscles around the eyes and mouth.

Do not remove a wedge of occipital bone as the dissector directs (pp. 193-194). A modification of this procedure will be performed later (Nose and Mouth).

Enlist the aid of an instructor in removing the brain. This will enable you to remove it in one piece while preserving the folds of dura matter. Do not split the brain.

DISSECTION 7. Eye and Orbit

Prepare for this dissection by reviewing the orbit on your skull. Pay special attention to the bony composition and the foramina connecting the orbit to the cranial body.

If the eyes have been removed from your cadaver, do not despair, you can perform this dissection without them! Most of the structures in the orbit remain after the eyes have been removed. Be sure you get to see the results of a dissection with intact eyeballs.

To remove the superior wall of the orbit in the anterior cranial fossa, you will probably want to use rongeurs (wonderful bone cutting tools that look a little like pliers) rather than chisels and probes. If you cannot find them, see an instructor. When removing this bone, you may want to continue your excavation more posteriorly and remove the bony lateral wall of the cavernous sinus so that you can examine the four cranial nerves and the internal carotid artery coursing through the sinus. You may find the ciliary ganglion and long ciliary nerves in the orbit if you are lucky. Do not feel crushed if you are not lucky.


DISSECTION 9. Pharynx and Larynx, Ear

Remove the head from the neck in the following manner. Using blunt dissection techniques, free up the visceral structures of the neck by moving them anterior to the pre-vertebral fascia. Using a sharp scalpel (i.e. new blade) cut through the deep posterior muscles of the neck, and move them aside to expose the craniovertebral joints. Cut through these articulations to separate the head from the vertebral column. The head will then be attached to the body only via the visceral structures of the neck, which can be moved forward. More details are found in the dissector (pp. 220-222).

If your cadaver has palatine or pharyngeal tonsils, do not remove them entirely as instructed by the dissector (p. 179). If your cadaver has no tonsils, be sure you try to observe one that does.

The dissector is accurate when it says that the otic ganglion is difficult to find.

Special dissection instructions for the ear are in syllabus.

DISSECTION 10. Infratemporal and Pterygopalatine Fossae, Nose and Mouth

Special instructions in syllabus for infratemporal fossa.

On one side of the head, dissect the infratemporal and pterygopalatine fossae. On the other side dissect the oral/nasal regions. The vessels and nerves of the region, and on the nasal septum, are small and can be difficult to find (believe it or not), so that you probably want to choose carefully on which side you perform the dissection of these structures.

Bisect the head as directed in the dissector (pp. 174-175), using a large hand saw. You might want to enlist the aid of an instructor before you begin. Make sure you cut through the posterior part of the skull to the foramen magnum and to the midpoint of the mandible, taking care not to obliterate the muscles in the floor of the mouth. Cut the tongue in half (lengthwise) and cut the floor of the mouth with a sharp scalpel blade. Do not cut into the epiglottis or pharynx.

DISSECTION 11. Thoracic Walls, Pleura, Lungs

Prepare for the lab by studying the bones of the thorax (ribs, sternum, and vertebrae) and surface anatomy. Read over the plan for dissection.

When you dissect, do not spend too much time on the dissection of the breast. The platysma and supraclavicular nerves were dissected with the neck.

Make the lower cuts in the chest wall along the course of the sixth rib, not straight across (p. 15). This will give you more room to see your work.

Do not attempt to identify every broncho-pulmonary segment, but do dissect at least one segmental bronchus and its accompanying branch of the pulmonary artery (p. 21).

DISSECTION 12. Heart and Mediastinum

Unless you are a masochist, do not look for the superior vena caval branch of the anterior right atrial artery (box on p. 28).

Realize that although the conduction system is functionally important, it is not readily dissectable. Do not spend time attempting to dissect it.

Do not spend a lot of time looking for the thymus (p. 35). Since most of our cadavers are bodies of elderly people it will usually be unrecognizable.

DISSECTION 13. Anterior Abdominal Wall and Inguinal Region

Prepare for the lab by studying the bony landmarks and surface anatomy of the abdominal wall and inguinal region. Make sure you understand the anatomy of the inguinal canal before you begin. You may want to make a model of the inguinal canal using paper, tape, string, and an articulated skeleton or using A.D.A.M. in the library to help yourself understand what is going on.

You should have a pretty clear idea of the descent of the testes through the inguinal canal and be able to explain how the coverings of the testes are derived during this descent.

Do not spend a lot of time looking for fatty (Camper's) and membranous (Scarpa's) fascia.

Before you enter the peritoneal cavity, read about the peritoneum, and make sure you understand all of the general remarks on p. 54 of the dissector.

Make sure that you see a dissection of the inguinal canal on a cadaver of different sex than yours. You will be required to demonstrate only on your cadaver.

DISSECTION 14. Abdominopelvic Cavity

The key to this region is to understand the grand plan of the arterial blood supply, the collateral circulation, and the venous drainage of the viscera in the abdomen. Make sure you have a clear understanding of the schema before you start to dissect.

You do not need to examine the interior of the GI tract (pp. 71-72) unless you have a burning desire to do so. If you wish to do so, wash out the feces in the sink under running water.

When seeking the suprarenal (adrenal glands) the best way to find them is usually to follow the arteries which supply them.

DISSECTION 15. Pelvis and Perineum

Use the syllabus to prepare for and execute the lab.