Download Name: Cat Dissection Part I: external anatomy, muscular system

Name: _____________________________
Cat Dissection Part I:
external anatomy, muscular system, and sensory systems (15 points)
Today you will begin the dissection of the domestic cat, Felis catus. Seriously, that is the
real scientific name. First, let the cat out of the bag. Drain the formalin (preservative fluid) into
the container provided by your instructor. Lay your cat on its back [in the supine position] and
secure its arms and legs with string. Note: the joints are stiff because formalin removes water
from the tissues and hardens the muscles. First: a refresher on anatomical reference terms. Draw
a sketch of your cat as it looks now, and label your sketch with the following terms:
anterior, posterior, dorsal, ventral, medial, lateral, cranial, caudal.
Now draw two rough sketches of your cat: a sagittal section and a frontal section, and label these
sketches with the following reference terms: superficial, deep, superior, inferior, dorsal, ventral.
Sagittal Section
Frontal Section
External Anatomy
Now, examine the following external features of your cat: claws, nose, ears, eyes,
eyelids, nictitating membrane, teeth, tongue, hard palate (remove the sponge from the
mouth), soft palate, incisors, canine teeth, premolars, molars.
Read the “dissecting technique” section on the next page before making any incisions.
Dissecting Technique
Before beginning the dissection of a given area, study illustrations in order to familiarize
yourself with the structures you will encounter. Use a sharp scalpel to make incisions in skin or
tissues, but you should never apply much pressure to a scalpel. The thin metal blade may easily
break, which can be dangerous. Hold a scalpel like a pencil and cut slowly. After making a
small incision in skin with a scalpel, use scissors to extend the cut. The blunt side of the scissors
should be facing down so as not to damage any internal organs. Use your sharp probe to scrape
connective tissue and separate organs from each other. Also use your scissors to trim away fat
(yellow, globular tissue) from internal organs. Then study and identify the individual muscles or
organs as they are listed below. Make sure you do not cut anything unless it is absolutely
necessary. You should not remove any organs from the cat unless your instructor tells you to.
Remember, when in doubt, you should err on the side of caution. You can always cut something
more, but you cannot undo a cut.
Skinning
Most dissections begin with skinning the organism to study the muscular system just
under the skin. Begin by making a shallow midventral cut (near the sternum) through the skin
with the scalpel and extend the incision with your scissors from the jaw to the anus. Be careful
not to cut through the thin muscle of the abdomen. If your cat is a female, cut around the nipples
and dissect the skin away from the mammary glands, which lie between the skin and the
superficial muscles of the abdomen.
Separate the skin from the underlying muscles by blunt dissection. Make additional cuts
as necessary to remove the skin from the torso and legs, leaving it intact around the mouth, eyes,
ears, and feet. These areas have much more connective tissue, and are therefore too timeconsuming to separate.
Fascia
As you pull the skin away from the body, you will observe that it is connected to the
underlying structures by a white, fibrous membrane consisting of elastic fibers and fat. This
layer of connective tissue, termed the superficial fascia, is distinguished from the deep fascia,
the tough fibrous membrane which invests the individual muscles.
Muscular System
Identify the following list of muscles. Try to separate each individual muscle from its
neighboring muscles by blunt dissection. Confirm the origin and insertion of each muscle.
Pectoralis major, latissimus dorsi, trapezius, biceps brachii, triceps brachii,
palmaris longus, masseter, biceps femoris, gastrocnemius, rectus abdominus.
Sensory/Nervous System
Identify the following list of sensory and nervous structures: cornea, iris, sclera, pupil,
ear, tongue, pads of the feet, sciatic nerve, radial nerve, ulnar nerve.
When 10 minutes remain in class, put your cat into a plastic bag to preserve the moisture. These
specimens will not rot, as they have been preserved with formalin. However, the tissues will dry
out over time, so the bags must be closed securely with a rubber band.
Name: _____________________________
Cat Dissection Part II:
Digestive system and other visceral organs (15 points)
Let the cat out of the bag again. Before making any cuts, you can identify some digestive
structures. Identify the parotid gland, submaxillary gland, and sublingual gland. What is the
purpose (or should I say… purr-puss) of these glands? I’ve got plenty more bad jokes where that
came from.
Image of
salivary
glands
Next, we will open the abdominal cavity by making a very small incision in the medial
part of the rectus abdominus muscle. Keep this incision shallow by dragging your scalpel blade
gently and pulling on the muscle laterally with your forceps until you are completely through the
muscle. You will also cut through the parietal peritoneum, the membrane that lines the
abdominal cavity. This membrane is continuous with the visceral peritoneum, which lines the
visceral organs. Extend the incision with the scissors cranially to the diaphragm, then laterally
around the sides of the abdomen. The visceral organs are now visible. Identify the following
digestive organs and structures:
esophagus, stomach, liver, gallbladder, common bile duct, pancreas, mesentery, duodenum,
jejunum, ileum, colon (large intestine), rectum, anus.
Make a quick sketch below showing the relative location of the organs, and label your diagram.
You can also see the large, dark-colored spleen on the left side of the abdominal cavity
(the cat’s left). You should also be able to see the urinary bladder, which lies ventral to the
rectum.
Cut the esophagus just above the lower esophageal sphincter. Begin removing the gut by
cutting the peritoneal membranes, which anchor it to the abdominal cavity. It will be necessary
to also cut through the common bile duct to separate the pancreas, gallbladder, and liver from the
duodenum. Do not completely remove the intestines—they should remain attached to the body
at the posterior end.
Dorsal to the intestinal tract, you should see two kidneys, with adrenal glands near their
anterior ends. The kidneys are attached to the urinary bladder by two tubes called ureters.
Draw a diagram below showing the two kidneys (their relative shape, size, and location
in the cat’s body), the ureters, and the urinary bladder.
If your specimen is a female, you should also be able to see two distinct horns of the
uterus, each attached to an ovary. If it is a male, you can observe the testes (singular: testis),
which are attached to the urethra by the ductus deferens.
Is your cat a male or a female?
Now cut into the thoracic cavity, which contains the lungs and the heart. This cavity is
separated from the abdominal cavity by the diaphragm, a concave, sheet-like skeletal muscle.
Notice that the esophagus goes through the diaphragm.
The two lungs are connected to the trachea (windpipe) by two tubes called bronchi. Cut
into one of the lungs, and describe its texture and internal structure here.
The heart is surrounded by a membrane called the pericardium. Cut open the heart
carefully and identify whether it has 2 chambers (like a fish), 3 chambers (like a frog), or 4
chambers (like a human).
Trace the esophagus to the mouth by inserting a blunt probe in the posterior end (which
you cut earlier). Where does the esophagus pass through the thoracic cavity?
Using only words, how would you describe the arrangement of the organs in the thoracic
cavity? Try to use correct anatomical reference terms.