Internal Examination

While browsing Thorndike's collection, I noticed the "Handbook of R.H. Burne's Cetacean Dissections." Although the book is from 1952, and costs "two pounds two shillings," there are many diagrams representing cetacean anatomy, along with muscle transects, anatomical pictures, etc. These visual aides are invaluable, especially to someone who is a novice to anatomy. Using Burne's book, I will detail the cetacean skeletal system tomorrow, focusing primarily on differences between human anatomy and that of the cetacean. First, however, I would like to wrap up WHOI's guide on cetacean necropsies, by going over the internal dissection, noting any contrasts between the already-covered pinniped necropsy.

The left flipper must be removed after the integument. This will allow for the locating of the prescapular lymph node, which should be peach/tan colored. It is relevant to mention, here, that College of the Atlantic does not perform necropsies with the same rigor and thoroughness that, say Wood's Hole, does. Due to our limited resources and education-focus, histology, virology, and other testing does not often occur. We are most adept at noticing macro-pathologies, such as conspicuous ulcers, impactions, etc. That is not to say that special care and attention is not given to these specimens, but merely that our abilities on-campus are limited and that sampling is less prevalent (although blubber was taken for sampling during the last harp beater necropsy). So although we would not usually preserve the prescapular lymph node for testing, it is still worthwhile to find it. The left scapula is removed by cutting through the connective tissue and muscle that is just under the bone while pulling the scapula down. A cracking sound should be heard during this removal.

The diaphragm is deflated before removing the rib cage. Again, there should be a sweet spot that is easy to cut through. Cut down the rib cage cranially. The cranial ribs are mostly double-headed, possessing two articulations, the first of which is cut, while the scalpel sweeps down the rib towards the vertebrae. The thyroid, tracheobronchial lymph node and thymus (only in juveniles, just like seals) can then be located. The lungs, like the liver in the abdominal cavity, occupy the majority of the thoracic cavity and are normally bright pink with a sponge-like texture. The lung can be detached from the trachea at the bifurcation which forms the bronchi. The trachea is longitudinally cut. Examination of the heart takes place exactly as it does for seals. Exposing the abdominal cavity is as easy as slicing mid-ventrally from the rib to the anus, cutting laterally along the thoracic arch. The liver is also lobular and is a deep maroon color. The spleen varies among cetacean species. Delphinids have a palm-sized and spherical spleen that is a "mottled dark purple to white color". Other cetaceans may have similar spleens, or they may be smaller or more ovoid. The spleen is located underneath the stomach towards the left side of the body. Accessory spleens may also be found. They act as smaller versions of the spleen. The pancreas is attached to the mesentery and sits in the curve of the duodenum. Procedure is the same for examining the mesentery, adrenal glands, kidneys, reproductive system and bladder in cetaceans and pinnipeds.

A thin tissue surrounds the stomach and is called the omentum. The stomach itself is made up of three compartments in most odontocetes. There is a fore stomach, a main stomach and a pyloric stomach. Each stomach should be examined by cutting along the greatest curvature, contents collected afterwards. The mucosa of each stomach is distinct. The fore stomach has squamous tissue that is usually white, while the main stomach has a stratified, dark red inside surface. The pyloric stomach is thinner, and is either pink or stained with bile. The remaining digestive system is then examined, followed by the brain and pituitary gland, with the same protocol as..you guessed it..the seal. An ear extraction can also be done, with protocol found in Ketten et al. (2007)




Citations:
Ketten, D.S., Cramer, S., Arruda, J. (2007) Procedure for the Removal, Fixation, and Preservation of Cetacean Ears. pp. 3.1-3.22