Where the _tendons_ of the various muscles pass over the wrist, both front and back, they are covered with a synovial sheath and are held down by a broad ligament, which some of them perforate, the annular ligament. The strong fibrous band of the _anterior annular ligament_ arches over the carpal bones in front. Beneath it pass the median nerve and the tendons of the flexors of the fingers and thumb. The _posterior annular ligament_ is of less importance. The deep _palmar fascia_ forms a sheath for the muscles of the hand. In carpenters there sometimes occurs _Dupuytren’s contraction_ of the palmar fascia, which draws the fingers up. As operation is not always successful, it is quite a serious matter. The _muscles of the hand_ itself include various abductor, adductor, and short flexor muscles of the thumb and little finger. There also extend between the metacarpal bones the _lumbricales_, four small muscles that aid the deep flexor muscles; likewise seven _interossei_, of which four are dorsal and three palmar. The _dorsal interossei_ arise by two heads from the adjacent sides of the metacarpal bones and are inserted into the bases of the first phalanges, thus abducting the fingers; while the _palmar interossei_, arising from the palmar surface of the second, fourth, and fifth metacarpals, are inserted into the three corresponding first phalanges and adduct the fingers toward an imaginary line drawn through the middle finger. =Joints of the Upper Extremity.=--The joints of the upper extremity, with the exception of the wrist-joint, are the most freely movable of any in the body, probably because the hand has the finest work to do and a greater number of motions are required. Even the wrist has much greater freedom of motion than the corresponding joint in the lower extremity. 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_.