Dissecting the Cat1

Introductory Exercises to Dissecting the Cat After completing this exercise, you should be able to: 1. Prepare the specimen for future dissections by removing all fat, fascia, and fur from the muscle surface so that muscle outlines and fiber direction can be seen. Materials The following materials should be provided for class use.1. Cats in plastic bags 2. Dissecting tools a. Heavy-duty scissors b. Scalpel c. Probe d. Two dissecting needles e. Forceps 3. String 4. Rubber bands Laboratory Operating Procedure The ideal way to make a dissection of cat muscles is for each student to work with his own specimen. However, the expense involved and the difficulty in procuring that large number of cats usually results in two or more students sharing an animal. If this is the case, it is to be understood that each student does an equal amount of work. Laboratory grades are given individually and the dissection grade must be shared by those responsible for the specimen. For the safety of the student it is recommended that a heavy-duty nonrazor scalpel be used. Always point scissors away from you when cutting tissue, and be careful to keep fingers away from the scalpel blade. Dissecting Technique: Before beginning the dissection of a given area, read through the dissecting instructions and study the illustrations in order to familiarize yourself with the structures you will encounter. Then study and identify the individual muscles as they are listed in the text, freeing each one from the surrounding muscles. In order to define the limits of a muscle, use small scissors and forceps to trim away the overlying fat and fascia until you can see the direction of the muscle fibers. Look for a change in the direction of the fibers near the place where the edge of the muscle should be, and attempt to slip the flat edge of your scalpel handle between two separate layers of muscle at this point. If one layer separates easily from another you have your scalpel between two different muscles. Do not try to cut or force the separation of the muscles. If you are looking in the right place the separation will be natural. Most muscles do not attach directly to the bone, but rather by extensions of fascia. Connective tissue which binds a muscle to a bone is called a tendon. Connective tissue which connects one bone with another is called a ligament. The name aponeurosis is often applied to broad, flat tendon. The connective tissue which binds muscle together may be very tough and require cutting with scissors or a scalpel, or it may be so soft and fragile that it can be broken by running a finger between the muscles. Do whatever you can with your fingers, resorting to scissors or scalpel only when necessary. The older the animal is the tougher the fascia. If you have an old cat to dissect you will find that you have to work harder to separate muscles than you neighbor who happened to get a younger specimen. When it is necessary to cut a muscle in order to expose underlying structures, make your cut at right angles to the direction of the fibers and about half way between the origin and the insertion. Then pull back the two halves of the muscle completely in order to make a neat dissection. In some cases it is desirable to leave the cut portions of the superficial muscles intact so that they can be replaced to re-establish their natural relationships with the underlying structures. It is often helpful to confirm an observation made on the left side of the specimen by dissecting on the right. If you do this, leave intact the origins and insertions of any muscles you cut on the right and do not destroy any of the nerves or vessels, which will be studied later. FASCIA: Is 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. CUTANEOUS MAXIMUS: In the lateral thoracic area you will observe muscle fibers lying within the superficial fascia and attached directly to the skin. These fibers are part of the cutaneous maximus, which originates from the muscles of the axilla and from the ventral side of the abdomen and thorax, and inserts on the skin. It serves to twitch the skin, as in avoiding irritants. Cut through the cutaneous maximus and remove it. PLATYSMA: Another muscle which moves the skin will be found in the area of the neck and face. This is the platysma, which inserts on the skin around the ears, eyes and lips. In skinning the head and neck, refer to Fig. 15 and 16 and be careful not to damage the superficial veins and glands. As you skin the dorsal side of the thorax and abdomen observe the segmentally arranged cutaneous vessels and nerves passing from the dorsal body wall to the skin. Procedure: Once Cat has been skinned. One must be careful not to let the cat dry out since it is impossible to do a good muscle dissection on a dry animal. If during the course of the semester you find the cat is losing too much moisture, notify the teacher to add solution. This solution may be placed directly on the musculature, used to remoisten the skin, or placed in small quantities in the plastic bag before it is closed with string or a rubber band at the end of the lab period. The last step before beginning the dissection of the muscle is the removal of all extraneous material from the surface, such as bits of fat, hair, loose fascia, and remnant of cutaneous maximus muscle and platysma. If you have any doubt about the removal of any type of tissue, ask the instructor for advice so that you do not cut off something essential to your future dissection. You can always remove an unwanted substance from the surface at a later time, but you can’t reattach something you have cut off and thrown away. Always proceed slowly after giving each move careful thought. When the surface is properly cleaned off, you should be able to make out some muscle outlines and see the directions of the muscle fibers. Make certain that all cutaneous maximus and platysma have been removed. Have your instructor check your cat before going on. Once you have read all of the instructions above you are ready to begin: The following are the steps to the proper and orderly preparation and skinning of the cat to optimize its use for dissection. At the conclusion of each dissection thorough cleansing of instruments, desks, sinks and floors is extremely important. 1. LABEL BAG: place bag on a clean table with end you will open to the left (this will be the end with the larger margin of plastic beyond the heat seal.) On the opposite end right the names of students in group. Name your cat if you like. 2. DRAIN the FLUID: At the sink, with rubber gloves carefully cut open the plastic bag close to the heat seal. Remove cat tail first and squeeze out excess fluid from the cat’s fur by milking down from head to tail. Set bag aside, keep the outside of bag clean and free of cat fluids and parts. 3. LIE CAT on its BACK: These cats have been injected with color coded latex: red for arteries, and blue for veins. Note the latex injection sites on the neck of the cat. Try to include these cuts in the lines where you make your incisions. 4. SKIN THE HEAD CAREFULLY: Make an incision from the base of the neck to the right corner of the mouth, peel the skin away from the base of the ears. Peel the skin off as far as you can until you get to the base of the ears. Cut through the auditory canal (ear) you will be cutting off the cats ear. BUT BE SURE NOT TO CUT ANY MUSCLES!! Peel the skin off the scalp until you feel the rims of the orbits (eyes). Carefully separating the skin from the eyelids being sure you leave the eyelids on the cat. Cut close to the bone to separate lips from upper and lower jaws. Leave the entire nose on the cast by cutting around the nose until the skin has been peeled away. WHEN YOU ARE READY TO PUT CAT AWAY . ..... . 5. PUTTING IT AWAY: To store your cat, pull the skin over the nose, wrap in proper position, place cat in plastic bag, fold the bag long ways and press out air. Then twist the end, fold it over, and secure with 2 or 3 turn of a heavy rubber band. If you do not fold it the juices will leak out in to the box of cats. 6. CLEAN UP!! Wash dissecting tool thoroughly, dry them, replace in the kits, and return to their proper location in the storage box. Clean up all fur, fat, and stray pieces from your desk, floor sink and surrounding counter. Wash all surfaces and edges thoroughly removing grease.