The shoulder-joint is rather a deep joint, to allow of the varied motion required, and has a capsular ligament from the margin of the glenoid fossa above to the neck of the humerus below. The elbow, which is a hinge joint, has an anterior and a posterior ligament and two lateral ligaments, as is practically the case in all such joints. The wrist has several ligaments which, taken together, are capsular in nature.
Blood Supply of the Upper Extremity.—The blood supply of the upper extremity comes through the subclavian artery, which, on the right, springs from the innominate artery and on the left from the aortic arch. It remains one trunk as far as the elbow, though different names have been given to different parts. Thus, as it passes over the lower border of the first rib, it becomes the axillary, and at the lower border of the axilla, where it starts down the arm, the brachial. At the elbow it divides into the ulnar and radial arteries.
In its upper part the brachial artery lies internal to the humerus but below it is in front of the bone. The radial runs in a line from the middle of the elbow anteriorly to the inner side of the styloid process of the radius and is much exposed to injury in the lower third of its course, as when the hand is thrust through glass. On it at the wrist the pulse is counted. It is much smaller than the ulnar and winds around the outer side of the thumb to the palm, where, with the deep branch from the ulnar, it forms the deep palmar arch. The ulnar artery passes obliquely inward to the middle of the forearm and thence along its ulnar border to the palm of the hand, where it divides into the deep branch and the superficial palmar arch which supplies the four digital arteries.
From the axillary artery branches go to the chest wall and shoulder, the most important being the two circumflex arteries to the deltoid. The brachial has only two branches of any importance, the superior and inferior profunda, both on the upper arm, of course.
In case of hemorrhage compression can frequently be applied with the fingers where the subclavian crosses the rib or in the axilla, where the artery can be pressed up against the humerus.
Nerves.—The nerve supply of the shoulder comes chiefly from the anterior and posterior thoracic, the suprascapular, and the circumflex, these last going to the deltoid. The biceps is supplied by the musculo-cutaneous, the triceps by the musculo-spiral, and the brachialis anticus by both. Most of the flexor and pronator muscles are supplied by the median, while the posterior interosseous and the musculo-spiral nerves go to the extensors and supinators. The ulnar nerve supplies the hand largely.
CHAPTER XIII.
THE LOWER EXTREMITIES.
The lower extremities resemble the upper very closely in the arrangement of the bones, muscles, arteries, and nerves, though modifications occur, due to the difference in function of the lower limbs. There is one long bone in the upper part or thigh, the femur, and two in the lower part or leg, the tibia and fibula, while over the knee-joint is the patella or knee-cap. The ankle has seven bones and the foot nineteen like the hand.