Cat Dissection

Cat Dissection 3 A. Superficial Arm Muscles, Lateral Surface Begin with the upper arm. You have already dissected the clavodeltoid which, although not an arm muscle, does cover the anterior surface. The largest superficial muscle in the upper arm is the triceps brachii. It is make up of three distinct muscle with three heads of origin, but it has only one point of insertion. The large mass over the posterior surface is the long head of the triceps. Lying next to it on the lateral surface is the lateral head of the triceps. Free each of these muscles between origin and insertion and then transect the lateral head of the triceps. Pull back the cut ends to reveal the smaller medial head of the triceps and next to it the brachialis. Distal to the triceps medial head is an L-shaped muscle surrounding the elbow, the anconeus. The anconeus need not be dissected, but merley observed. It is usulually darker in color than the surrounding muscles, which helps in locating it (it is not found in humans). In the lower arm dissect only the superficial muscles. An extension from the brachialis of the upper arm is the brachioradialis. The muscles next to the brachioradialis in order are the extensor carpi radialis, the extensor digitorum communis, the extensor digitorum laterialis and the extensor carpi ulnaris. B. Superficial Arm Muscles, Medial Surface The medial surface of the upper arm is almost entirely covered by a broad, flat sheet of muscle, the epitochlearis and you will find the somewhat convex biceps brachii muscle beneath the pectoral muscle. In the lower arm begin at the anterior border with the brachioradialis previously observed. Lying next to it is the extensor carpi radialis which has two parts: a shorter, somewhat triangular extensor carpi radialis brevis and beneath it the extensor carpi radialis longus. The next superficial muscles to separate are the narrow pronator teres and next to it the flexor carpi radialis. The widest of the group and is called the palmaris longus. The last muscle on the medial surface is the flexor carpi ulnaris. C. Abdominal Muscles There are three thin layers of muscle covering the abdominal cavity. You must be careful in this dissection not to cut too deeply. Determine origin and insertion of the external oblique, the first layer, and mark off the midpoint with a pencil or other tool. This muscle must be transected to see the one below it, and the transaction line will be slightly curved due to the shape of the muscle. Begin the cut with the tip of the scissors and gradually extend it until you can get a probe between the external oblique and the internal oblique, the second layer. When you are sure that you haven’t gone too deeply, extend the transection line and separate as you go along with your fingers. Bring each half back to origin and insertion. Near the insertion on the linea abla (midline) you will see a long, ribbon like muscle, the rectus abdominis. Expose as much of it as you can. You can’t see the anterior part of the muscle at this time, but it will be seen in a later dissection. To separate the internal oblique from the transverse abdominis, the third or innermost layer, use extreme caution as both muscle are very thin. Sometimes the transverses abdominis is so thin that its fibers separate and you can see the parietal peritoneum (lining of the body cavity) between them. Separate as much of the internal oblique as you can and reflect the cut ends. Do not make your transaction line too close to the broad aponeurosis by which the muscle inserts. Note that the directions of the fibers of the external oblique and internal oblique are almost at right angles to one another. Cat Dissection 3 A. Superficial Arm Muscles, Lateral Surface Begin with the upper arm. You have already dissected the clavodeltoid which, although not an arm muscle, does cover the anterior surface. The largest superficial muscle in the upper arm is the triceps brachii. It is make up of three distinct muscle with three heads of origin, but it has only one point of insertion. The large mass over the posterior surface is the long head of the triceps. Lying next to it on the lateral surface is the lateral head of the triceps. Free each of these muscles between origin and insertion and then transect the lateral head of the triceps. Pull back the cut ends to reveal the smaller medial head of the triceps and next to it the brachialis. Distal to the triceps medial head is an L-shaped muscle surrounding the elbow, the anconeus. The anconeus need not be dissected, but merley observed. It is usulually darker in color than the surrounding muscles, which helps in locating it (it is not found in humans). In the lower arm dissect only the superficial muscles. An extension from the brachialis of the upper arm is the brachioradialis. The muscles next to the brachioradialis in order are the extensor carpi radialis, the extensor digitorum communis, the extensor digitorum laterialis and the extensor carpi ulnaris. B. Superficial Arm Muscles, Medial Surface The medial surface of the upper arm is almost entirely covered by a broad, flat sheet of muscle, the epitochlearis and you will find the somewhat convex biceps brachii muscle beneath the pectoral muscle. In the lower arm begin at the anterior border with the brachioradialis previously observed. Lying next to it is the extensor carpi radialis which has two parts: a shorter, somewhat triangular extensor carpi radialis brevis and beneath it the extensor carpi radialis longus. The next superficial muscles to separate are the narrow pronator teres and next to it the flexor carpi radialis. The widest of the group and is called the palmaris longus. The last muscle on the medial surface is the flexor carpi ulnaris. C. Abdominal Muscles There are three thin layers of muscle covering the abdominal cavity. You must be careful in this dissection not to cut too deeply. Determine origin and insertion of the external oblique, the first layer, and mark off the midpoint with a pencil or other tool. This muscle must be transected to see the one below it, and the transaction line will be slightly curved due to the shape of the muscle. Begin the cut with the tip of the scissors and gradually extend it until you can get a probe between the external oblique and the internal oblique, the second layer. When you are sure that you haven’t gone too deeply, extend the transection line and separate as you go along with your fingers. Bring each half back to origin and insertion. Near the insertion on the linea abla (midline) you will see a long, ribbon like muscle, the rectus abdominis. Expose as much of it as you can. You can’t see the anterior part of the muscle at this time, but it will be seen in a later dissection. To separate the internal oblique from the transverse abdominis, the third or innermost layer, use extreme caution as both muscle are very thin. Sometimes the transverses abdominis is so thin that its fibers separate and you can see the parietal peritoneum (lining of the body cavity) between them. Separate as much of the internal oblique as you can and reflect the cut ends. Do not make your transaction line too close to the broad aponeurosis by which the muscle inserts. Note that the directions of the fibers of the external oblique and internal oblique are almost at right angles to one another.