FOREARM AND HAND 127 



Short Muscles of the Thumb. The abductor pollids forms 

 the most prominent and lateral part of the ball of the 

 thumb. The superficial head of the flexor pollids brevis lies 

 immediately to the medial side of the abductor ; and by separ- 

 ating the one from the other, the opponens pollids will be 

 exposed. These three muscles lie to the lateral side of the 

 tendon of the flexor pollicis longus. To the medial side of 

 this tendon, and placed deeply in the palm, is a fan-shaped 

 muscular sheet, the adductor pollids, imperfectly separated into a 

 proximal and distal part by the radial artery as it enters the 

 palm. The proximal is the oblique and the distal the trans- 

 verse part of the muscle. 



In dissecting these muscles the muscular branch of the median nerve 

 must be traced to those which lie upon the lateral side of the long flexor 

 tendon of the thumb, and the deep branch of the ulnar must be followed, 

 and its branches to the adductors of the thumb secured. 



The abductor pollids arises from the volar aspect of the 

 transverse carpal ligament and the os multangulum majus. It 

 is inserted into the lateral side of the base of the proximal 

 phalanx of the thumb, and slightly into the extensor tendon 

 on the dorsum of the proximal phalanx. Its nerve of supply 

 comes from the median. 



The superficial head of the flexor pollids brevis 1 takes origin 

 from the transverse carpal ligament, and is inserted into the 

 lateral side of the base of the proximal phalanx of the thumb. 

 It is supplied by the median nerve. 



The opponens pollids springs from the transverse carpal 

 ligament and the ridge on the front of the os multangulum 

 majus. Its fibres spread out, and are inserted into the entire 

 length of the lateral border and the adjacent part of the volar 

 surface of the metacarpal bone of the thumb. Its nerve of 

 supply is derived from the median. 



The adductor pollids consists of two parts, an oblique part 

 (O.T. oblique adductor pollicis) and a transverse part (O.T. 

 the transverse adductor pollicis). The oblique part arises 

 from the os multangulum minus, the os capitatum, and the 

 bases of the second and third metacarpal bones. The 

 transverse part springs from the lower two-thirds of the volar 

 border of the third metacarpal bone. The two parts con- 



1 The term superficial head, applied to this muscle, suggests the presence 

 of a deep head. Such a head is present. It is the interosseus primus volaris 

 of Henle (v. p. 147). 



