184 THE UPPER EXTREMITIES. 



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 suc- 

 cessful, it is quite a serious matter. 



The muscles of the hand itself include various abduc- 

 tor, adductor, and short flexor muscles of the thumb 

 and little finger. There also extend between the meta- 

 carpal 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 



