Special Sensory Organs

My next entry is on what Burne labels the special sense organs. Cetacean sensory organs are remarkably different from terrestrial mammals, having undergone extensive aquatic adaptations. Most noteworthy, in my opinion, is the lack of an olfactory sense in most whales and dolphins. This degradation occurs in varying degrees; delphinids possess no olfactory perforations, while baleen whales have perforations of their mesethmoid bone (the most anterior bone of the braincase, corresponding with the cribriform (upper nasal region) plate found in mammals), although these only host simple nerves that connect to the nasal passage.

The lens of the eyes are highly convex in cetaceans. The posterior segment of the bulbus oculi (globe), which includes the back two-thirds of the eye, is relatively shallow. Both of these adaptations better suit the cetacean for aquatic vision. The margins of the cornea are thickened and the optic nerve is encased in ophthalmic rete to protect the fragile eye from general, and diving, water pressure. The tear gland (lachrymal gland) secretes a greasy substance in cetaceans, and along with the conjuctiva (exterior eye coating) which is replaced by, in some whales, a horny epithelium, protect against water damage.

The lack of external ears (pinnae) in whales is an easily noted but intriguing oddity. The internal ear is also highly adapted for aquatic life. The entrance to the ear is streamlined with the body, and only vestiges of the auricular cartilage are found in some whales underneath the integument. The tympanic membrane (eardrum) of baleen whales are quite distinct. Shaped as a long, hollow an conical structure, this membrane can be as long as 3 inches. An earwax plug extends out from the eardrum. Odontocetes have a traditional mammalian eardrum. In the tympanic cavity there are auditory ossicles that connect to each other. The ossicles occur in the following form going inwards: hammer-bone (malleus), anvil-bone (incus), and stirrup-bone (stapes). The malleus connects to the eardrum and is also fused to the tympanic bulla, while the stapes is located in the innermost wall of the middle ear (fenestra ovalis). These three ossicles form an irregular column between the tympanum and the inner ear. Tympano-periotic bones are the densest bones in the cetacean skeleton, the tympanic bulla the most prominent representative.

(Pictured: tympanic bulla of a cetacean)

The eustachian system, which connects the middle ear to the nasal passages of the pharynx is specialized in cetaceans. Baleen whales possess a sac (pterygoid sinus) that is found in the region of the pterygoid bone. These sacs (diverticula) are extremely specialized in dolphins and occupy much of the sinus region. Two diverticula are found along the roof of the mouth, reaching to an inch of the tip of the snout. In most mammals, such as humans, the eustachian system is barely even a system, comprising only a thin tube that is often closed. The specialization of this system in cetaceans, especially delphinids, is suggestive of the importance of hearing in these species for external contact. With the olfactory senses atrophied, cetaceans benefit from this additional sensory system for life functioning.

Well there you have it for special systems! This is likely my last anatomical entry; two seals and three necropsy reports need to be done (dissected and written, that is) in the next 2 weeks, and I still have to familiarize myself with human interaction sheets. I was surprised by how much anatomical jargon I was introduced to. Even simple terms like aperture and foramen were newly learned, and I am now comfortable with several systems I previously knew little about. I've also established a foundation upon which more anatomical lessons may be placed. I will post the necropsy reports once they are finished, but until then, ciao.

Cetacean Vascular System

The first topic I have selected for my end-of-term review is the vascular system of cetaceans. Note that in my review of pinniped thoracic cavity necropsy I covered the heart, gaining much insight into an organ I wasn't very familiar with. General vascular anatomy is an important topic to study, and I am sure there are cetacean adaptations that are worthy to note. I am consulting Cetacean Dissections (Burne, R.H.) for this review, and will follow the pattern of blood flow described in the book.

All venous blood is deoxygenated except for blood contained in the pulmonary vein (vein denotes any blood vessel whose flow is moving towards from the heart, and is not a characterization of oxygen content). This venous blood converges upon the caval veins (inferior vena cava and superior vena cava). The coronary sinus is located within the vicinity of the entrance of the inferior vena cava into the right atrium, and this collection of vessels drains blood from the myocardium into the right atrium. From the right atrium blood is shuttled through the tricuspid valve, and so forth into the rest of the heart (already detailed in seal heart post).

The retia mirabilia (wonderful net) is a system of closely located arteries and vessels. This system is especially pronounced in cetaceans and serves a variety of purposes. Countercurrent blood flow is created by placing core-warmed arterial blood next to distally-returning venous blood. This sets up a heat gradient that lowers the rate of heat dissipation, allowing the extremities to more gradually heat up or cool down depending on the situation. Burne also hypothesizes that the network of vessels is so elaborate as to allow continuous circulation during diving, as high pressures may restrict some arteries. Scholander (1940) argues that the retia might allow blood to be shunted past the muscles, which are high in myoglobin concentration and would rob arteries of their oxygen content before their blood load arrived to vital areas. The book becomes dated when Burne explains that there is an "observed absence of a diving brachycardia (bradycardia) in the Cetacea." Noren and Cuccurullo (2004) is just one example out of many of observed bradycardia in cetaceans. Although this does not discredit Burne's hypothesis, it does show that this book is indeed from the 1950's. Retia mirabilia appear throughout the body at key areas, such as the thoracic cavity (thoracic retia mirabilia), which is found in between the heads of the ribs and which extend into the spinal canal. This connects the arteries of the chest wall with those that supply the brain.

Finally, a fascinating insight into the formation of the heart in utero is also given by Burne. While the lungs are inactive, the two sides of the heart are still connected. Communication between the right and left side is done through the foramen ovale, a partition between the two atria, thus by-passing the pulmonary artery and the lungs. This blood contains a mixture of arterial blood carried through the umbilical cord and impure blood from the fetal body. Even with the inter-atrial aperture, some blood does pass into the right ventricle and then on into the pulmonary trunk. Were it not for another by-pass between the pulmonary artery and the aorta (ductus arteriosus), this blood would reach the lungs. When the first breath is taken at birth the foramen ovale closes and becomes a slight depression (fossa ovalis), while the ductus arteriosus shrivels into a ligament (ligamentum arteriosum). During the fetal stage, the lungs are supplied with the blood necessary for growth byh bronchial arteries which extend from the aorta, and these arteries continue to nourish the lungs even after birth.

Citations:

Scholander, P.F. (1940) Experimental Investigations on the respiratory functions in Diving Mammals and Birds. Hvalradets skrifter, 22: 1-32. Oslo.

Noren, S.R. Cuccurullo, T. M. (2004) The development of diving bradycardia in bottlenose dolphins (Tursiops truncatus). Journal of Comparative Physiology. Vol. 174. 2. pp. 139-147.

Change of Plans

After meeting with my trusty advisor, Sean, it was concluded that for the remaining duration of this independent study I will be producing necropsy reports on the seals I have and will necropsy. These in-depth reports will sharpen my vocabulary, prompt valuable investigatory explanations, and give me something tangible to present in addition to this journal during my independent study evaluation. Because time is so limited and at least 2 more necropsies need to be performed, these journal entries will become less frequent and will focus only on select topics I deem necessary. These select topics are what I perceive as gaps in my anatomical knowledge and include the nervous, endocrine, and circulatory systems in cetaceans as preliminary front-runners. My current collection of books (previously noted in this journal) will be consulted alongside new finds to produce the most efficient and specialized course of study for this limited time period. Finally, although I have extensively reviewed necropsy protocols, my familiarity with the actual Human Intervention forms is lacking. Writing these necropsy reports will undoubtedly help with accustoming me with these forms, but direct studying will also occur.

There's a lot left to do, so wish me luck!

Cetacean Skeletal System

Cetaceans trace their evolutionary history back to the archicetes, and even further back to a common ancestor with the Artiodactyla (even-toed Ungulates such as deer, camels and cattle). Formerly land mammals, whales and porpoises have gone through extensive morphological and physiological changes to adapt to their aquatic environment. Looking at their fusiform shape, complete with (in many cases) a dorsal fin, it is easy to see why these mammals were once thought of as fish. Water imposes the same environmental constraints upon the fish and dolphin, hence they have convergently evolved to the morphology that is best suited for aquatic locomotion. The skeletons of cetaceans are so striking because they are so strikingly different from land-based organisms, yet distinctly mammalian. It is as if every possible mammalian bone has been morphed, while still remaining identifiable.

The general shape of these whales, as mentioned briefly before, is designed to offer the least resistance to movement in water. The head, which usually tapers off towards the snout, passes into the trunk without a definable neck. The dorsal fin is positioned near the center of the body in most odontocetes, occurring towards the lower third section of the back in larger whales. The dorsal fin is entirely cartilaginous, held up by strong ligamentous fibers and a fibrous core. The flukes provide primary movement, and is also absent of bone, except for the distal end of the backbone which lies between them.

Forelimbs are flattened and shaped into fin-like paddles most often referred to as flippers. The scapula (shoulder blade) is broad and flattened, and has an acromion and coracoid process which articulate from the scapular body in a flat projection. These two processes may occur in different shapes, or be absent from some species of cetaceans. An example of this is the humpback whale (Megaptera novaeangeliae) which is wanting of both the acromion and coracoid processes. Similarly, the clavicle is missing in all cetaceans.

One of the oddest structures of the cetacean skeleton is the lower flipper. Digits are still clearly demarcated and are found all within the same integument. The metacarpals and phalanges are indistinguishable from each other, but the phalanges occur more distally and can be identified in that sense. The first digit, known as the pollex, may be missing from certain species such as the blue whale (Balaenoptera musculus) resulting in a more slender fin. The phalanges are equipped with epiphysial cartilage at each end which is replaced by bone as the animal grows. The phalanges and metacarpals are attached to the wrist bones (carpalia, or carpals), which are cartilaginous in the juveniles of some species. These bones are in turn connected to the elbow joint, which does not allow much motion between the upper arm and the fore-arm, and is often fused together in elderly whales. The fore-arm is comprised of the ulna and radius, while the upper arm refers to the humerus. The humerus is a short bone whose head articulates with the scapula. The distal end of this bone is comparatively flattened and terminates in two facets to meet the fore-arm bones. These bones are also short and flattened, and reside parallel to each other. The proximal end of the ulna is known as the olecranon, and is a a hatchet-edge projection that occurs proximally.

External hind-limbs are completely absent in all cetaceans, but a vestigial pelvis remains. This pair of pelvic bones has no contact with the vertebral column, and the femur and tibia range in presence throughout species. Sperm whales (Physeter macrocephalus) are the only odontocetes to possess a femoral vestige, the rest of the toothed whales lacking all hind-leg bones.

The cranium is strongly compressed from front to back and appears globular. The rostrum is often elongated and serves as a beak in various delphinids. The seven cervical vertebrae are highly compressed, and may be fused in differing order in various species. Transverse processes are well developed in the lumbar and caudal regions, and diminish in size towards the tip of the tail. The chevron bones, which are "ventral V-shaped elements faceted to the under surfaces of contiguous vertebral bodies," articulate between the hind end of one vertebra and the fore-end of the next.

Rib count is also variable between species, 12-16 pairs the normal amount. The Southern Bottlenosed Whale (Hyperoodon planifrons) has the least number of pairs of all mammals, with only 8. The sternum is composed of several fused elements, with species-variable numbers of ribs attached. For example, the breast-bones of Mysteceti are only large enough to attach to the first pair of ribs.

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

External Cetacean Necropsy

As much of WHOI's guide for pinniped necropsy is similar to that of cetaceans, I will be reviewing the latter section with more haste so that I can focus on advanced topics. This will also give me a chance to contrast seal and whale necropsies.

The external exam begins just the same as the pinniped's, by examining the carcass' condition. Before beginning, it is important to remember that stranded cetaceans are outside of their natural habitat, and thus apparent pathologies may actually be produced by the juxtaposition of a heavy, marine mammal in a foreign and inhospitable environment. Lacerations, bruising, organ compression and fluid pooling are to be expected, especially on long-dead specimens. Fresh carcasses (code 2) will have been stranded for less than 24 hours, while code 3 bodies will exhibit bloating, skin sloughing and other signs similar to that of the seal. Code 4 and 5 range from a collapsed carcass to mummified remains. Body condition is assessed by examining the dorsal side of the cetacean. Epaxial muscle of a robust animal is convex and rounded, while a thin animal will have a slightly sunken in girth. Emaciated cetaceans will exhibit concaveness and may have indentation of the nape.

Sex determination in cetaceans is slightly harder to do than for pinnipeds, in my opinion. the ventral midline will show a genital slit between the umbilicus and anus for both males and females. Positioning is the difference. Females should generally have their slit within 10 cm from their anal opening, while males have a greate distance. Short mammary slits may be found on either side of the genital slit in females, but may also be found in some males, and thus is not the best physical marker. Genital probing (using your finger, not weird alien equipment) can also be used. If your finger angles forward, the vagina has been entered, and if backwards, it is the penile opening. The penis may also be felt in this manner. Species differences may complicate this, but if all else fails, internal examination will reveal the truth.

Removing the skin & blubber: The cetacean should be positioned left-side up (as opposed to a ventral-side up in pinnipeds). Using a scalpel, a longitudinal incision should be made posterior to the blowhole and going down the dorsal midline, ending at the tail. Cutting perpendicularly, make 25 cm panels down the rest of the animal, making sure to make one panel under the axilla. Reflect the blubber away and cut through the fascia, revealing the skeletal muscle. Bruising in the skeletal muscle usually has a gelatinous texture and appears as a deep red or purple. The large epaxial muscle that powers the stroking action of the cetacean is then removed, along with any excess muscle on the backbone and ribs.

Next entry will tackle all of the internal anatomy of the cetacean.

Harp Seal Necropsy

This Friday, a recently thawed beater harp seal (Phoca groenlandica) was necropsied by me and a team of students and Allied Whale employees. The seal was hit by a car in its head, shattering large parts of its mandible, skull and maxilla. The force of the impact caused the seal to defecate (feces were found around the perianal region, although death was probably (and hopefully) instant. Fur from its front flippers was missing, suggesting that the beater had crawled for some time before reaching the road. Besides the cranial damage, the rest of the seal seemed to be in good shape. Concavity of the pelvic region suggested that the seal was slightly thin, but not emaciated. The presence of a penile opening clearly identified the seal as a male.

The necropsy began by removing the integument, Amanda Dunn and Michelle Klein accompanying me. The front flippers were then removed, but not before I spotted the prescapular lymph node (which I suppose I was overly excited to find). Amanda took the right and I took the left. We opened up the abdominal cavity next. A green fluid (bile?) was found inside the mesentery around the large intestines, but the intestines overall looked healthy. The kidneys were remarkably reniculated, and one showed damage in the form of lacerations (source unknown).

The thoracic cavity was then opened, and I am sad to say I failed at finding the sweet spot (mid articulations of the ribs), mostly likely due to the positioning of the carcass slightly on the right. The lungs were thoroughly soaked in blood, most likely post-mortem. The heart appeared fine, and the aorta was characteristically a pale beige. Due to the chaos of trying to remove the rib cage, I overlooked finding the diaphragm. We incised the trachea, which appeared healthy, and removed the head from the body. The extent of damage to the head was profound. Bits of skull and maxilla were resting on the tongue, and the skin of the head easily slid off the bone. The brain was clearly impacted from the force of the bones snapping back dorsally, and the teeth were sunken into the gums.

After we disposed of the carcass, everyone scrubbed-out and went home. Most of the blood had been drained before the necropsy began, both in the bag it was held in and at the accident site, so this was probably one of the cleanest necropsy's I will ever witness. I was grateful to have a code 2 body to work with, and even more appreciative of the help I received. Thank you to Spencer, Leah, Rosie, Jessica, Michelle, Amanda and especially to Jackie for helping out! Below are some pictures (courtesy of Ms. Klein)

Thawing out a frozen seal

With just 2 days pending until my first planned necropsy, the dead beater harp seal that was recently run over by a car is now in the Arts & Sciences building. I hope it thaws. I also hope it stays there. Logistically, this has been a little frustrating. As Jackie has complained to me about, we need a necropsy lab, or at least a time block that is only for Allied Whale in the Zoology lab. Oh well, this is a small school, you make what you need out of what you have.

There was also a stranding response to two other seals and a long dead whale, the latter found fairly decomposed in Corea, Maine, just a few miles away. Me and Amanda Dunn may head out there one of these days to collect a bone for identification...that is if we can figure out how exactly you cut up a frozen whale. I don't think it will be a smooth as a hot knife through butter. In other news, I have attempted to read the neurobiology section of The Biology of Marine Mammals. I have found the jargon and anatomical terms a bit too complex for this stage in my independent study, however, and so I will focus on more basic anatomy of the nervous system. The brain itself is wonderfully complex, and exists in varied shapes in both pinnipeds and cetaceans.

Next week I will start on cetaceans, but for now I'll just review necropsy techniques in preparation for this Friday, and watch the snow lightly fall on bar island.

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.

Pinniped Necropsy: Abdominal Cavity

As noted earlier, the diaphragm separates the thoracic cavity from the abdomen. By now, both cavities will have been opened, and the dissection should proceed with the removal of the liver. The liver is multi-lobular and maroon. Located over the stomach, the liver is fairly large in pinnipeds, encompassing the majority of the abdominal cavity. The liver should be removed before the gall bladder is incised to prevent contamination, and the parenchyma can be examined by bread-slicing (this technique will come in handy for viewing the inside of most organs). Examine the color pattern and texture of the lobes and parenchyma, all the while searching for parasites (especially in bile ducts).

The gall bladder is a round and green organ that is located ventrally between the right and central lobes of the liver. The gall bladder is a thin walled sac that stores and secretes bile. By cutting into the duodenum (first part of the small intestines), it can be determined whether or not the gall bladder is secreting bile. Check for gall stones. The spleen is a slightly discoid, but mostly oblong purple-white organ found underneath the stomach along the left body wall. Pinniped spleens may be serrated or have irregular margins, a normal sight. Examine the organ and bread-slice. The pancreas is located in the curve of the duodenum and is a lobulated, peach-colored tissue. Look for changes in color in the parenchyma and examine the ducts for parasites. Furthermore, the pancreas is attached to the mesentery, a translucent, malleable but firm connective tissue that is in turn attached to the intestines. Examine the mesentery for any adhesions, and note if there is congestion of the vessels. Lymphatic vessels may be distended with a milk-like fluid if the seal has recently eaten. The mesenteric lymph node can be found centrally on the mesentry and is a large, finger-like lymph node that tends to have a more pronounced cortex and medulla than previously described lymph nodes. As is usual, note any changes in the interior (by cross-section cutting) and exterior aspects of this lymph node.



Next, locate the right and left adrenal glands in situ, as they may be hard to find without the kidney as a guide. These two glands are located anterior to the cranial pole of each kidney, and are small, maroon tissues with irregular furrows over their surface. Pull the tissue distally and cut connecting tissue to remove the adrenal glands. Measure and weigh each adrenal gland and then cut them in half. The medulla should be distinctly darkened, with a lighter cortex. Look for the aperture of the medulla. A normal, pen-tip sized opening indicates usage of the glands. The kidneys are a darker shade of maroon and are reniculated (possessing miniature kidneys). They are attached to the caudal dorsal abdominal wall and are enclosed by the capsule, a connective tissue. Longitudinally incise the capsule and reflect each half to reveal each kidney. Detach them from the abdominal wall and examine the internal and external structure, making note of any stones. also observe the medulla:cortex ratio and the degree of differentiation between the two. Normal reniculi are clearly demarcated and clustered together within the kidney.

The bladder is a relatively small, light pink and found anterior to the pelvic bone along the ventral body wall. If urine is present in the bladder, it may appear thin and slightly translucent, as opposed to a thick-walled appearance when not full. Extract urine aseptically from the bladder, noting the amount, color and consistency, and then remove the bladder. Cut along the length of the organ to expose the mucosal surface and note the color of this mucous.

In past necropsies, most notably the harp seal (P. groenlandica), the stomach held the greatest clues for cause of death, and so special care must be taken to ensure that the stomach is thoroughly analyzed. Tie off both ends of the stomach with twine before removal, one knot at esophagus-stomach interface, the other just below the duodenum. Cut beyond both knots and then examine the serosal (external) surface of the stomach, noting any lesions, or changes in color. If there is a pathological condition, the perigastric lymph node may be enlargened. Incise along the wall with the greatest curvature, and note the stomach contents. These contents can range from food, to fluid, parasites, or even foreign objects. Collect a sample and then run the contents through a sieve to collect solid materials that may have gone unnoticied. Photograph any foreign objects and save them. Now empty, the stomach lining can be examined. Note the mucosa and look for ulcers, parasites and lesions. Weigh the stomach when it is emptied.

The intestines are the last of the abdominal cavity organs to be examined so that they do not contaminate the body. The small intestines should be serosally examined, areas of hemmoraghing or discoloration noted. The inside can be examined by spot checking: select 5-10 random areas and then cut down 10 centimeters of their length, noting color, contents, thickness etc. The large intestines are located by finding the ileo-ceco-colic junction, which is a ridged section between the small-diameter small intestines and the large intestines. Repeat spot checking for both the large intestine and the colon. A sample of feces should be taken from the colon for toxicology analysis.

The last topic to tackle in Pinnipeds is the nervous and reproductive systems. As the endocrine system is spread out all over the body, the relevant glands associated with these systems will be covered, too. Pituitary gland, my eye is on you.

Cardiovascular Adaptations

Perusing the how-to necropsy guides has been an indispensable use of study time, but to keep learning fresh and to gain further insight into marine mammal anatomy I have started to consult other books. Andersen, H.T. (1969) The biology of marine mammals., has proved a very concise and intriguing source, and lists separate anatomical subjects in chapters. As I was covering the cardial tissues last, I skipped to the corresponding section in Andersen regarding cardiovascular adaptations to diving. Much of this chapter seemed to be review, as I have covered diving adaptations in previous classes (Sperm Whale Diving Adaptations, Marine Mammal Biology I; The Weddell Seal, Polar Ecology and Exploration), but I did appreciate Andersen's inclusion of the history of diving adaptation discovery in marine mammals, and his comparisons to terrestrial mammals. I was less grateful for all the descriptions of forcibly submerging and drowning mammals, but who has time to delve into ethical attitudes of the 1960's.

I won't repeat the cardiovascular adaptations here, as my previous papers do a fairly good job of explaining the profound ability of cetaceans and pinnipeds to dive, but I think it is worthy to note several insights the chapter provided. Vasoconstriction is a critical requirement of marathon diving, whereby bloodflow slows and even halts in the peripheral and distal vessels. This lessens the overall oxygen demand, maintaining high levels of oxygen in the organs and tissues most vital to survival and feeding (esophagus, brain, heart). Much of the skeletal muscle, too, is deprived of oxygenated blood during these long dives. While this may seem counterintuitive, as the animal needs to be able to use its muscles to swim, it makes perfect sense in practice. Myoglobin is highly concentrated in muscle tissue and has a higher affinity for oxygen than haemoglobin. If blood flow were not slowed past these muscles, the myoglobin would rob the blood of its oxygen, preventing it from traveling to the aforementioned vital organs. Marine mammals have an incredible tolerance to high blood pH and lactic acid buildup, so their muscles can still operate under anaerobic conditions for the duration of the dive.

What really struck me was how tight this separation between peripheral vessels and muscle was from the main bloodflow. Lactic acid levels were shown to remain at steady levels during the dive, but dramatically rose once the animal had surfaced, before gradually tapering off again. This clearly illustrates the ability of marine mammals to separate parts of their body that are anaerobically respirating from the parts that are reliant on oxygen.

Harrison, R.J. (1971) Functional Anatomy of Marine Mammals., is another source I consulted, but after browsing its chapters, it was clear that Harrison tackles mostly advanced and specialized topics on select marine mammals. This book will come in handy when a certain species requires additional attention, but as a day-to-day guide, there are better options such as Andersen and Dierauf. Speaking of Dierauf, I found a free Internet copy of the Pinniped Forensic, Necropsy and Tissue Collection Guide.

The Pinniped's Heart

By now we have observed all of the organs of the pluck except one: the heart. The pericardium is the sac that contains the heart, and this should be trimmed away to see the epicardium (external surface of the heart). A small amount of clear fluid is contained within the pericardium, which allows for lubrication during normal heartbeat activity. If there is a lot this fluid (pericardial effusion), and if it is off-colored, make a note of it as this may indicate a wide variety of cardial issues such as pericarditis (inflammation of the pericardium), complications from tuberculosis, trauma, etc.

The mammalian heart is separated into 2 ventricles and 2 atria. Deoxygenated blood flows from the ventricles directly into the right atrium, where the tricuspid valve then shuttles it into the right ventricle. The pulmonary valve shuttles this blood into the pulmonary artery, which passes by the lungs. Oxygenated blood then travels from the pulmonary vein into the left atrium where the mitral valve is, and then this blood is sent into the left ventricle, then through the aortic valve and into the arteries and aorta where it is sent throughout the body. All of the valves, ventricles, atria and the aorta and pulmonary valve should be examined and noted for any inconsistencies during the necropsy. This can be accomplished by removing the heart from the aorta and pulmonary artery by cutting the two transversely, leaving 6 centimeters of each vessel still attached. To examine the internal structures, two methods can be utilized:

Using scissors, make a small incision in the right atrium and cut along the peripheral edge going towards the apex (lowest part of the heart), then following up the right ventricle side of the septum until you reach the pulmonary artery. Then cut the left ventricle side of the apex, go along the septum until the aorta is reached. This leaves both sides of the heart intact, but is fairly complicated. A simpler way is to slice the entire organ in half starting from the apex and then travelling laterally towards the vessels.

The pulmonary artery is a flappy vessel that enters the right atrium cranially while the aorta is the most muscular and tough artery. Both should be cut longitudally and examined for defects. The left atrium and ventricle should have thicker and more muscular walls than the right side (thickness ratio of around 2:1), with the left ventricle the thickest part of the heart. The right pulmonary vein and right atrium are the most flaccid. Unusual structures within the chambers of the heart may suggest hereditary illness or vestigal fetal structures. They, along with lesions should be recorded. The myocardium can be examined by bread-slicing the ventricles.

And that was the heart! While I was initially intimidated by the intricacies of the heart's anatomy, it was more straightforward than I thought it would be. Next entry will explore the abdominal cavity. Then the pinniped part of this study will be complete and we can move on to small cetaceans.

Inner Organs: Thoracic Cavity

In my previous post, I accidentally omitted the procedure for removing the rib cage. In order to reach the tracheobronchial lymph node, and the other organs of the thoracic cavity, this step is necessary. The abdominal organs are first exposed by making an incision on the abdominal wall mid-ventrally at the site of the last rib. Cutting cranially along the thoracic arch, reflect the abdominal musculature as you go along. The thoracic cavity is then opened by trimming away muscle attached to the rib and deflating the diaphragm by puncturing it. Note if there is deflation, as an absence of deflation can suggest severe pneumonia. It is important to note that the diaphragm is a large structure that separates the thoracic cavity from the abdominal cavity, and once punctured, will deflate healthy lungs due to positive ambient air pressure invading a previously air-proof cavity. The rib cage is then removed by cutting through each thoracic rib mid-articulation (also known as a sweet spot). This is a flex point made of cartilage whose purpose is to allow movement during breathing. Cutting cranally, the ribs should also be reflected, revealing the thoracic cavity.

Pinnipeds have comparatively larger thoracic cavities than their terrestrial distant relatives. This was especially apparent during my last necropsy on a gray seal (Halichoerus grypus), as that specimen's neck was almost as long as the rest of its body. This is congruent with the seal's opportunistic diet, as it must be able to seize any size of fish possible. The esophagus found in pinnipeds has the attributes of extreme flexibility and elongation, a necessity to process large prey.

Organs in the thoracic cavity can be removed and examined separately, or be removed together. The latter situation involves removing the tongue, larynx, trachea, esophagus, bronchi, lungs and heart and is termed the pluck. This procedure enters through the head, as skin is peeled off the chin and neck and then the sides of the mouth are cut open, the incisions extended caudally to the thorax. While pulling the tongue, the connective tissue and muscle holding the pluck is snipped until everything falls loose. I witnessed this on my first necropsy of a harp seal (Phoca groenlandica) and it was performed by a veterinarian. Thus it is my guess that until a vast amount of practical experience is accrued, I will not attempt this particular method. Maybe someone will prove me wrong..

As noted before, healthy lungs may collapse when the diagraphm is deflated. These organs are large and conspicous in the thoracic cavity, and will normally have a bright pink color and sponge-like texture. The lungs can be detached at the bifurcation of the trachea and then examined. Pressing down on the lungs, gauge if they bounce back, as normal lung tissue will act sponge-like. Additionally, healthy lungs should float if placed in water or a formalin solution. Translucent connective tissue connects lobules in pinniped lungs, and this tissue can become filled with gas in a pathological condition known as emphysematous. Using scissors, cut along the bronchioles of each lung and note if there are parasites, fluid, etc. Next, by bread-slicing you can further eamine the tissue. Make parallel slices perpendicular to the long axis of the body, and is best accomplished by a swift and single cut. This will allow you to view the bulk of the organ (parenchyma) and note any deviations from normal color/texture without any tears or serrations. The trachea should also be examined by cutting longitudinally along the entire length and then examining any mucus or other fluids.

My next post will deal with the heart. I am consulting further texts beyond the necropsy guides to further my knowledge of the heart because I honestly don't have a full grasp of the mammalian heart. Until then, ciao.

Internal Examination: Lymph Nodes

With the external layers now peeled off and disposed of, the inner cavity of the body and its organs can be examined. Pinniped Forensic Necropsy and Tissue Collection Guide (Dierauf, L.A. 1994) arranges the abdominal cavity inspection directly after blubber and excess muscle are removed. Woods Hole Oceanographic Institution's guide (Pugliares, et al. 2007) recommends an examination of several glands before the body cavity is opened. This order is congruent with that of previous necropsies I have attended and is thus the mostly likely procedure I will encounter while at COA, and since the WHOI's guide is more recent, it likely represents the most current and agreed upon necropsy technique.

Prescapular lymph node: To access the prescapular lymph node, the front flippers will need to be removed. With the subject ventral side up, pull the flipper away from the body and cut through the connective tissue all the while searching for the prescapular lymph node. This lymphatic organ is normally oval, beige or peach colored and firm. Deviations from this template may indictate disease or dysfunction, and should be recorded. The cortex (outer layer) and medulla (center of lymph node) may differ slightly in coloration. This is normal.

Thyroid: The paired thyroids can be found along the lateral sides of the cranial trachea and are distinguished by their dark purple color and flat and disk-like shape. The texture should feel like smooth muscle (for a comparison, feel the stomach or esophagus). As these glands are among the most important in the endocrinal system, any abnormalities should be noted. The parathyroid can also be isolated and sampled. This light colored tissue will be located on the cranial side of the thyroid and is important in regulating calcium.

Thymus: This organ can be found mainly in neonates, although some juveniles and adults have vestigal remnants. The thymus is absorbed after weaning and thus will be difficult to find in adult individuals. If a young of the year or neonate is the subject of the necropsy, however, the thymus can be located at the base of the thoracic inlet (superior thoracic aperture), bordering the cranial side of the heart. (Fun note: Sweetbreads are actually just the thymus of butchered livestock. Gross.)

Although there are other glands (tracheobronchial lymph node, mesenteric lymph node) they will be described alongside the organs they accompany in the body-cavity examination. With the rib cage now exposed, the next step will be to, like the blubber, reflect the ribs away to examine the lungs, heart and other viscera.

Removing External Layers

To begin the internal examination, the blubber, skin and muscle of the seal must be removed. In some otariids such as the Antarctic fur seal (Arctocephalus gazella) blubber thickness will be reduced, while pelage may be sparse on others such as odobenids. Placing the animal ventral side up, slide a scalpel from under the chin continuing down the midline to the anus, making sure the cut incises down to the muscle-blubber interface. To avoid the penile opening in males, course slightly left. From the midline incision, make perpendicular cuts 15 centimeters apart down the entire length of the animal. Using a hooker, hook on to the panels of flesh and pull distally. A scalpel can then be use this tension to reflect the flensed blubber away from the body.

During the blubber removal, special care should be made not to penetrate or pucture the skeletal muscle or the body cavity that lies underneath. Note any inconsistencies between the preliminary blubber thickness measurements and what is seen during the blubber reflection process. Also record texture and color of the blubber layer. If there are parasites, lesions, bruising or anything other than creamy white to light pink and firm blubber, it too should be noted. The panels of blubber should then be removed and skeletal muscle then examined. Any abnormalities of the muscle mass or fascia should be recorded as excess muscle is trimmed away from the rib cage.

Pinniped Morphologic Assessment: Pre-Necropsy

With the ice seal stranding season currently underway, knowledge of how to properly necropsy pinnipeds is of primary importance and thus will be my foyer into functional anatomy. Referencing Pugliaries as was done in the first entry, I began on external examinations. Since otariids are not found in the North Atlantic, this entire entry will apply only to phocids, as there are morphological differences that cannot be generalized to both families.

Assessing the condition of a pinniped carcass is a necessary pre-necropsy step, as this can dictate which tests can be done. For example, bacterial tests may only be done on fresh carcasses due to a high probability of contamination in moderately or heavily decomposed specimens. There are five code categories that a stranded seal may fall under:

Code 1: Alive.
Code 2: Fresh carcass
Code 3: Moderate decomposition
Code 4: Advanced decomposition
Code 5: Mummified or skeletal remains

Distinct morphological changes accompany each respective stage, such as bloating evident in moderate decomposing individuals. This can be exhibited by a protruding penis or tongue, and is further differentiated from a fresh carcass by dry mucous membranes, cracked skin and a mild odor. Advancedly decomposed specimens may be found intact, but are severely collapsed, have liquefied internal organs and emit strong odors. Scavenger damage is also often apparent. Mummified or skeletal remains are self-explanatory.

Nutritional Condition: By observing the neck and pelvic regions of a stranded pinniped (deceased or alive), a general assumption about that animal's nutritional condition can be made. This spectrum can range from robust to thin to emaciated. Emaciated individuals exhibit conspicious ribs, protruding pelvic bones and have a visible neck. A healthy, robust individual will appear rounded and have a fusiform body shape. In thin animals, the neck and pelvic bones will show slightly. Blubber thickness measurements will further elucidate any nutritional deficiencies during the necropsy.

Sex Determination: The gender of a specimen can be determined by examining the animal ventrally. Lactating females have two horizontally spaced, off-centered teats found caudal to the umbilicus. These mammary glands are not always conspicous and may be obscured by pelage. Non-lactating females have even less obvious teats, sometimes only observable as spots of baldness. Females have two openings, the anus and vagina, in the peri-anal region found near the hind flippers; males only have an anal opening. The penile opening can be found on the ventral midline caudul to the umbilicus, as is true for females. Further help in determining sex can be given by palpating the ventral surface in search of the os penis.

Integument Analysis: The final external assessment before necropsy involves a thorough examination of the pelage, skin, orifices (ears, eyes, etc.) and genitals. Discharge, swelling, lesions, parasites, mucus membrane color, missing teeth, etc. should all be noted. Mammary glands should be palpated to express milk, color, consistency and amount (in cc's) also noted. Regions commonly affected by human interaction such as the peduncle, axilla, or snout should be given particular attention. Skin from between the 1st and 2nd digit of the left rear flipper should be removed, 2 inches the standard amount. The entire lower left jaw is also removed for aging. By cutting the mandibular symphysis from the rostrum to the last post-canine teeth (front of snout to throat), the left mandible can then be dislocated from the zygomatic arch through the trimming of connective tissue and muscle.

In the next few days I will be researching internal examination, utilizing Dierauf, L.A. in addition to Pugliares, K.R.

Bienvenue a mon blog.

C'est ma première entrée et non, this journal will not be in French (although if I were truly ambitious, this independent study would encompass both marine mammals and the language). Instead, this marks my first entry for my winter of 2010 independent study (my first!) in Applied Marine Mammal Anatomy. The term is rather short for what I plan to study, but essentially I will be distilling anatomical textbooks into a functional approach to necropsies. There will hopefully be a lot of blood in the next coming weeks, as I have signed on to the necropsy team (thank you Rosie), and there are some long-frozen specimens in our on-campus freezer. For now, there are no definite dates, but I should at least start introducing myself to necropsy techniques. My main source these first few weeks will be Marine Mammal Necropsy: An introductory guide for stranding responders and field biologists. (Pugliares, K.R. et al.)

Due to the stochastic nature of strandings, I should be prepared to respond to potential necropsies as soon as possible, and so for this first week I have decided to sidestep an introduction to anatomy and first delve into how to record data for necropsies as well as preliminary sample techniques and data collection. My previous necropsy experiences have introduced me to safety protocols such as utlizing protective gear, sanitizing not only myself but all areas which have come in contact with the specimen during the necropsy, and immediately reporting any cuts that may occur when handling sharp knives/other equipment. These necessary safety measures will be repeated during every necropsy, training and thus proficiency learned through repetition. After all, studying is less likely to cultivate a solid knowledge in safety protocols than practice.

The goal of any necropsy preformed in the United States is to ascertain whether or not human interaction (HI) has affected the specimen. This does not necessarily mean that HI was the direct cause of death, or that because a specimen died of natural causes HI is not present. There are many variables to look at when necropsying, pre- and postmortem injuries just one example, and so it is imperative that when I perform necropsies there is an awareness of these numerous conditions. Objectivity and a conservative eye are indispensible if I want any sort of credibility, and being a liberal college student, this is especially true. With this small but important reminder to myself I begin the more technical route of my studies. Ethics and necropsy logistics merit their own study and attention, but for this independent study I must remember my primary focus.

Morphometrics - To begin to understand how a specimen has come to lie on the necropsy table is to first look at its physical attributes. Details such as age estimations and reproductive status can be determined by examining the weight and length of the specimen and comparing it to known life history stages of each respective species. With time and experience, a clear understanding of what constitutes for example, a young of the year harp seal, emerges and identification can be efficiently correct and swift. For now, this is not something I need to worry about, as more-experienced guides such as Rosemary Seton are around to lend their expertise as I train. Cetaceans are measured from the maxilla to the fluke notch, while pinnipeds are measured from the tip of the muzzle to the end of the tail. Both pinnipeds and cetaceans should face ventral side down while these measurements are done. Pinnipeds require an additional measurement, a curvilinear total length which is measured by laying tape on the top of the dorsal midline, starting at the tip of the nose to the end of the tail while following the body's contour.

Blubber thickness can be an important health status marker for pinnipeds and cetaceans. Unlike length and weight, this measurement is taken in millimeters and is recorded from the muscle-blubber to the skin/fur-blubber interface. Three 2-3 inch long dorsal to mid-ventral cuts are made: the first is made to intersect the dorsal midline, the second to intersect the lateral midline, and the last to interesect the ventral midline which should be made along the axillary plane. Skin and fur thickness should not be included with the measurements.

Well, that marks the end of this first week's introduction to necropsies. Starting next week I will delve into pinniped necropsy techniques, anatomy and tissue sampling. This topic should hold me for about the next 3 weeks and will be accompanied by more traditional studying of anatomy with topics such as the skeletal and muscular system. Until next time, au revoir!