- tending the whole thumb, the others only a part. They
rise from the ulna and radius, not the condyle. The extensor communis digitorum goes to all the phalanges of all the fingers, the extensor minimi digiti to those of the little finger only, and the extensor indicis to those of the index finger, the last two arising short of the condyle.
Of the supinators the longer one is inserted into the styloid process of the radius, while the shorter one, the supinator brevis, is inserted into the upper part of the same bone, both thus serving to turn the radius on the ulna.
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
