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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.