Anatomy of the muscles that move the arm

Of the arm muscles, that is, the muscles that move the shoulder joint, three muscles come from the chest and pull the arm down. The origin of one of them is under the nipple, and it is adjacent to the front of the arm at the anterior edge of the clavicle cavity. This muscle brings the arm closer to the chest, lowering it downwards and dragging the shoulder along with it.

Another muscle grows from the top of the sternum and runs around the inside of the head of the humerus. She brings her hand to her chest, lifting it slightly; further, there is a large double muscle, which begins on the entire sternum and is adjacent to the lower part of the anterior end of the humerus. Acting with the fibers of her upper part, she brings her hand closer to her chest and raises it; when the fibers of the other part act, this muscle brings the arm closer to the chest, lowering it, and if both parts act together, the arm approaches the chest in a straight position.

Two more muscles grow from the side of the ilium, they penetrate deeper than the large muscle that rises from the sternum.

One of these muscles is large. It comes from the ilia and from the posterior ribs and pulls the hand towards the posterior ribs in a straight position.

The second muscle is thin; it comes from the skin of the ilium, and not from the ilium, more than the previous one, deviating towards the middle, and adjoins in depth the tendon of the muscle rising from the side of the nipple. The second muscle acts in the same way as the first, acting as an assistant, but only it leans slightly back.

Five more muscles grow from the scapula bone. One of them grows from the bone of the scapula and occupies the space between the spine and the upper edge of the scapula. Passing to the top of the outer end of the humerus and deviating slightly inward, it moves the arm away from the chest, deviating inward.

Two of these five muscles begin at the upper edge of the scapula. One of them, the large one, sends its fibers to the lower part of the scapular spine and occupies the space between the spine and the lower edge of the scapula. It adjoins the head of the humerus far from the outside and moves the arm away, deflecting it outward.

Another muscle is adjacent to the first, forming, as it were, part ^ee, passes along with it and produces the same effect, but only this second muscle is not very connected with the upper part of the scapula. It adjoins, going obliquely, to the outer part of the humerus and deflects the arm outward.

The fourth muscle occupies the concave place of the scapula, its tendon is adjacent to the inner parts of the medial side of the head of the humerus. The action of this muscle is to rotate the arm backwards. Another muscle starts from the lower end of the lower edge of the scapula. Its tendon attaches to the arm above the large muscle that rises from the ilia. Its effect is that it pulls the top of the humerus upward.

The arm also has another muscle, the biceps. Its heads perform two independent actions and one common for both. This muscle comes from the bottom of the clavicle and from the neck, surrounds the head of the humerus and approaches the place where the tendon of the large muscle that rises from the chest adjoins the humerus. They also say that one of the heads of this muscle is located inside and deviates inward, going slightly obliquely, and the other head is outside, on the back of the shoulder blade, at its bottom, and it deviates outward, going slightly obliquely.

When this muscle acts in both its parts, it raises the arm in a straight position. Some people add two more muscles to their arm muscles; a small muscle coming from the nipple, and another hidden in the joint of the shoulder. Sometimes it is attributed to a general action with the muscles of the elbow.