Cat Shoulder

For comparison, see the shoulders of a ferret, a bat, a fox, and a tree shrew.

Dissection Techniques:

Removing the skin was challenging, because the fur stuck on the muscles, and made them difficult to see. For this part of dissection, mid-sagittal cuts were made dorsally and ventrally from about C1 to about L1. Transverse cuts were made from where the sagittal cuts ended, in order to remove the skin from the body. The skin was displaced and the furs that were sticking onto muscles were removed with wet paper-towels in order to make the dissection and viewing the musculature easier. The muscles were identified with a probe and superficial muscles were reflected for viewing the deeper ones. This specimen had short limbs, but the musculature was well developed.

General Anatomy:

- A cat is a digitigrade quadruped. A cat has a large head relative to its body size and a short neck. This cat was missing its tail.
- A cat has eyelids (palpebrae) and nictitating membranes, which are white membranes that could be seen by opening its eyes and probing the medial corner of the eyes.
- As the skin was removed, there were some fascias that separated muscles from the other muscles. The thin white layer of fascia separating the muscles was visible.
- Some cutaneous branches of the nerves and arteries were visible during the process of removing the skin. Laterally, the branches of posterior subscapular nerves were visible between armpits.

Shoulder Dissection:

Cutaneous muscles are the most superficial muscles. They come off with the skin when it is removed, especially the cutaneous maximus muscle, which is a thin muscle that is attached to the skin and wraps around the entire trunk of the animal. Thus extra caution is needed in order to see these cutaneous muscles separate from the skin. A cat has a well-developed platysma muscle. This muscle inserts onto the facial structures, especially the eye and the mouth. In order to view this muscle, some facial skin needs to be removed, and the entire muscle is not visible unless the skin from the mouth and the eye area are removed (this is another lab). The platysma muscle seems to be stronger than the cutaneous maximus muscle, which is absent in humans. Also, compared to other mammals, such as the ferret or the tree shrew, the cat seems to have more prominent platysma muscle.

Once the cutaneous muscles are cut and reflected, if they did not come off with the skin, then the other superficial muscles are visible. On the dorsal side of the cat, the trapezius muscles and the sternocleidomastoid muscles are visible. There are three parts of the trapezius muscle: acromiotrapezius, clavotrapezius, and spinotrapezius. Much of the posterior portion of the acromiotrapezius muscle is merely a thin aponeurosis lying over the vertebral column and connecting the right and left trapezius muscles without other attachment. This muscle is hard to separate and easy to rip off. Therefore it is easier to identify this muscle and separate it from others by figuring out the direction of the fibers using the pointy probe. The clavotrapezius muscle is also difficult to define, because at first look, it seems to be the same muscle as the acromiotrapezius. However, this muscle is more cranial to acromiotrapezius muscle, and also visible from the medial side.
All pectoralis muscles are superficial shoulder muscles. They are visible immediately when the cutaneous maximus muscle is cut and reflected on the ventral side. Pectoralis muscles in the cat are different from that of humans. In a cat, the pectoantebrachialis muscle is a small strip of muscle. It is just superficial to the pectoralis major muscle, and it has no homologue in humans. The xiphihumeralis muscle also is absent in humans. This muscle is caudal to the pectoralis minor muscle, and even though this muscle is thin, it is broad. The pectoralis major muscle in cats is often divided into a superficial portion and a deep portion, but they both insert on the humerus. However, this muscle tends to vary in cats, sometimes showing three or four parts. This cat had two divisions for this muscle. Both muscles are clearly visible, when the pectoantebrachialis muscle is cut and reflected. However, the deep portion of it is visible even without having the pectoantebrachialis muscle reflected. The pectoralis minor muscle is larger than pectoralis major in cats, while in humans it is relatively small. The pectoralis minor of the cat is caudal to the pectoralis major muscle, and it frequently seems to be divided into anterior and posterior portions. This cat had only one portion. The pectoralis muscles are significant in cats, but compared to that of a rabbit, it was less significant, since the rabbit had such a well-developed pectoralis muscle.

The latissimus dorsi muscle is also a superficial shoulder muscle on the dorsum of the body. This is a large muscle wrapping around the trunk, and it is easy to tear it off accidentally with the cutaneous maximus muscle. Then, there are deltoid muscles, which are significantly smaller than that of a rabbit, but still powerful. The acromiodeltoideus muscle is cranial to the spinodeltoideus muscle and is easy to miss. The spinodeltoideus muscle, however, is easy to spot. It lies medial to the triceps muscle.

The supraspinatus and the infraspinatus muscles are part of the deeper shoulder muscles. These two muscles are easy to locate on the dorsum of the body. If the scapula is held out, the muscle attaching to it in the medial side of the scapula can be seen. The muscle attached at the superior position is the supraspinatus and the inferior one is the infraspinatus. Both are thick muscles, and the supraspinatus is a bit more significant in size than the infraspinatus. Locating the teres major is difficult, because this muscle is very small in a cat and because it looks like a part of the latissimus dorsi muscle. It is a tiny strip of muscle lying cranial to the latissimus dorsi muscle. However, this muscle seems to be more prominent in other animals. The muscle that is cranial to the teres major is the subscapularis muscle. It is a large muscle covering the scapula on the ventral side.

The rhomboideus muscle in a cat has an interesting feature. It is divided like spaghetti straps, but it is seen as one muscle. This muscle is well developed in a cat, and it is homologous to both the rhomboideus major and the minor muscles of human. A cat has also a large serratus ventralis muscle to hold its limbs in upright position as other quadrupeds do. This muscle has a serrated look, but this cat does not have as serrated feature as the rabbit does.