Completing the Pinniped Necropsy

Week 4 is almost to a close, I am busy reading about thermoregulation in marine mammals (Andersen) and reviewing the proper necropsy procedures for the nervous/reproductive system.

Females: By following the reproductive tract from the vagina up, the ovaries, fallopian tubes and uterus can be found. The uterus will be a tan-pinkish color and depending on the sexual maturity of the specimen, can vary in size and thickness. Reproductive history and trauma may also alter the appearance of the uterus. Examine the internal and external surfaces, noting all the usual characteristics (by now you should know, Danny). Pregnant females will contain a fetus that can also be necropsied if it is large enough. If the fetus is of sufficient size to be examined, incise the abdomen and extract lung tissue, performing the same floating test as was done for adult tests. If the lung tissue floats in water, bronchiole expansion of the lungs has occurred. If the fetus is too small to necropsy, preserve it in formalin.

The left and right ovaries are attached to the end of each respective uterine horn and will appear as off-white and spindle shaped. Detach them to further inspect. Corpus albicans will be present on mature ovaries, while corpus luteum will be present on a pregnant female's ovaries. Weight and measure each ovary and count the number of scars. Examine internally.

Males: The testes are also spindle shaped and off-white and are located outside of the abdominal cavity along the ventral body wall and proximal to the ventral hip bones. This is evolutionarily advantageous as sperm production is often a function of temperature, and regulating temperature is easier away from the variable heat-producing viscera of the abdominal cavity. Remove the testes and weigh/measure them, examining both the organ itself and the epididymus inside and out. Check for the presence or absence of sperm in the epididymus and obtain a sample if possible.



The last part of the necropsy is also the most delicate, as it involves a fragile and extremely important organ: the brain. A lot of the techniques described in WHOI's guide are meant for seasoned necropsiers, so I also doubt I will take the lead on hack-sawing the skull, but detailing the process is still necessary. I will quote the more detailed parts of this procedure.

The first step to removing the brain is to detach the head from the body. This is accomplished by cutting behind the base of the skull between the first vertebra and the occipital condyles (facets of the occipital bone, the major lower pentagonal bone of the cranium). To help this separation, pull the muzzle towards the ventrum (middle of the body). Once detached, the excess integument can be trimmed away from around the caudal and dorsal sides of the skull. "Then, using a Stryker saw or a hack-saw, make cuts from left to right through the middle of each occipital condyle, then up along the left and right lateral skull, and then across the dorsum, just caudal to the marked transverse ridge at the apex of the skull." Then carefully position a chisel between the pentagon-shaped cut and turn it to crack the remaining bone until the dorsal cranium breaks off. Pull this section off evenly, without using one edge as a lever, to prevent bone from entering the brain tissue. Using your fingers, try to remove the meninges (membranes that protect the nervous system) away from the skull and go around the brain severing cranial nerves. The now-disconnected brain should fall into your hand once inverted.

At this point, handling should proceed gingerly, as the brain is at risk of falling apart. Note symmetry of the brain's structure, look for parasites and record color and texture. Separate the brain into two hemispheres by cutting cranially to caudally. The distinct sections of the brain have their own patterns; the cerebrum has two separate lobes and is the forward-most part of the brain. The cerebellum is the most caudal portion, and the brain stem starts from the ventral midline and then extends down to the spinal cord. The pituitary gland can then be located back on the carcass, and is found under the crossover of the optic nerve. Incise the overlying dura (outermost layer of the meninges) and find the bony recess that is the pituitary gland.

And there you have it! Next week, with Sean Todd back from England, and Jackie Bort and Amanda Dunn to help out, we will hopefully remove one of the seals from Allied Whale's freezer and perform a necropsy. I expect small cetacean necropsies to go along somewhat like the pinniped's, and so there will be less of a detailed description for the porpoises and more emphasis on comparative anatomy/specialized systems/miscellaneous topics. I have isolated the nervous system as another area where I could use more review and so I will consult Andersen and other library sources. After all, this is the first time I heard the terms dura and meninges (although I now understand where the meningitis gets its name). Until next time, ciao.