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Dissection of the Cat External Anatomy

Spend a few moments examining the external features of your cat. The following discussion covers the most obvious features. It is important that you know the references to orientation of the cat used in all lab manuals. Ventral: analogous to cats "belly" viewed when the cat is lying on its back. Dorsal: the cats back viewed when the cat is lying with the ventral side down on the tray. Anterior: The "head end" of the cat. Posterior: The "anal end" of the cat/ Left and right lateral: The sides of the cat ... when standing on all fours that is the "outside of the leg". Left and right medial: The sides of the cat... when standing on all fours that is the "inside of the leg". Like most mammals, the cat is almost completely covered with a dense coat of hair. Hair, composed of keratin, is a uniquely mammalian feature. The primary function of mammalian hair is to provide insulation. By "fluffing" the hair with the arrector pili muscles attached near the base of the follicle, the cat is able to trap a layer of air next to its skin. This is warmed by the body and serves as a barrier against the colder air adjacent to the fur. When cats are threatened, they "fluff" their hair in an effort to appear bigger, a form of intimidation. Color patterns in the fur of domestic cats are merely random effects of genes, with no obvious benefit to their survival. As you recall, all calico cats are females, the color being controlled by genes located on the X chromosomes. It is rare to obtain exotic breeds in the lab (Persians, Siamese, etc) since they are usually adopted while the more mundane are euthanized.


A secondary function of the cat's hair is to serve a sensory role. The cat has about its mouth, cheeks, and eyes stout long hairs called vibrissae. These have a sensory function (touch), allowing the cat to "feel" its way through darkness and judge distances between objects to discern if the body will fit. Other important sense organs located on the head include, eyes, ears, and nose. Their functions are self-evident. The external nares, "nostrils" are separated by a groove, the philtrum, which forms a cleft in the upper lip. In humans, the philtrum is normally closed and flat. The eyes are located toward the front of the head, producing stereoscopic vision (both eyes can focus on a single point). This allows the cat to develop "depth of field" perception, which is important in judging distances, an ability critical to predators. Primates also have stereoscopic vision, an adaptation that permits them to leap from branch to branch (miscalculation of distance could have very negative consequences). Cats are not colorblind. Mammals are the only animals with pinnae, external ear structures. These earflaps protect the ear opening and more importantly reflect sound into the middle ear. Cats can pivot the pinnae to "point" at a sound source. Cats have excellent hearing, although in my cats it seems to be very selective. Mammalian digits (fingers and toes) are equipped with claws, hooves, or nails. The cat's claws are usually clipped to reduce the risk of injury during dissection. Occasionally one will find a cat that has been declawed, a sure indicator that it was once a beloved pet. On the under surface of each foot are epidermal thickenings called frictional pads or tori. These cushion the step and provide traction. Cats have exceptional balance and are able to twist their body when falling so that they "usually" land feet first. Mammals are animals with mammary glands. Cats have two rows of about five mammary glands each. Look for the nipples to the left and right of the mid-ventral line. Even the males have these glands, though obviously they do not function. The density of the fur may make them difficult to locate; however, try to find at least one. The cat's post-anal tail is well developed and assists in balance. Occasionally they are broken or missing, as result of "shipping and handling". The anus, the posterior opening to the digestive tract, is located


just ventral to the cat's tail. You need to locate this opening; "somewhere under there" is not an acceptable identification. The external genitalia are the external sexual structures. Cats are difficult to sex since they show very little sexual dimorphism; although for "ally cats" the mature males are usually much larger. If you have a female, the urogenital aperture "the opening to the female's reproductive tract" is just ventral to the anus. You should be able to place the probe directly on the opening during the quiz. At a similar location in the male is the scrotum, a sack containing the testes. My favorite cat was named Scrotum. In cats that have been neutered the "sack" may not be distinct. Immediately anterior to the scrotum is the prepuce, a slight swelling in which the penis is retracted. We will dissect that out another day. Note that only primates lack a protective sheath around their penis allowing it to be visible at all times. Before cleaning up from this session, make a label so you can retrieve your cat for future dissections. Provide your cat with a name. Names such as Garfield, Morris, and Felix are highly unoriginal, reflecting a total lack of creativity on your part. Also naming your cat after the instructor is generally frowned upon. A name based on fur color (i.e. Spot), might lose its meaning since the next session involves removing the skin. Remember to wash your hands ... before you go to the bathroom.

This is not a cat!

Dogs are not dissected for several reasons: · Everyone loves dogs... not so for cats. · More importantly, if I ordered 10 dogs I might get five poodles and five St. Bernards.



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