THE RADIAL REGION 215 



The Radial Region 



The following muscles constitute the thenar eminence and have 

 a great variety of description. (See Quain and Henle.) 



1. M. Abductor Pollicis (brevis). Origin, front of the annular 

 ligament, ridge of the trapezium or tuberosity of the scaphoid; 

 insertion, base of the proximal phalanx of the thumb, radial 

 border, and sends a slip to the extensor tendons. (Henle 

 calls this one belly, and what is described below as the outer 

 head of the flexor brevis he calls the other belly of the abductor.) 



2. M. Flexor Brevis Pollicis. Outer or superficial head 

 rises from the outer two-thirds of the annular ligament, 

 inserts on the outer side of the base of the proximal phalanx, 

 having a sesamoid bone developed in it; inner or deep head 

 is very small, and between the adductor obliquus and outer 

 head of the first dorsal interosseous ; rises from the ulnar side 

 of the first metacarpal; inserted into the inner side of the base 

 of the proximal phalanx. 



3. M. adductor pollicis Quain describes in two parts, separated 

 by the radial artery as it enters the palm. The adductor 

 obliquus pollicis (caput obliquum, p. n.}, largest of the thumb 

 muscles, rises from the upper ends of the second and third 

 metacarpals, os magnum, anterior carpal ligaments, and 

 sheath of the flexor carpi radialis; it passes on the inner side 

 of the long flexor tendon to insert on the inner side of the base 

 of the proximal phalanx, uniting with the adductor trans- 

 versus and deep head of the flexor brevis. The inner sesamoid 

 bone is developed in it. A considerable fasciculus passes behind 

 the long flexor to join the superficial head of the flexor brevis 

 and outer sesamoid bone. (This muscle is usually described 

 as the inner head of the flexor brevis.) 



4. The adductor transversus pollicis (caput transversum, 

 p. w.) rises from the lower third of the front of the third meta- 

 carpal bone; inserted into the inner side of the base of the 

 proximal phalanx of the thumb, and the common insertion 

 sends a slip to the long extensor. 



5. M. opponens pollicis beneath the abductor, rises from 

 the annular ligament and outer side of the ridge of the trape- 

 zium; inserted by an upper layer into the whole length of the 

 first metacarpal bone, radial border, and by its deeper layer 

 into the head of the bone and radial part of its palmar surface. 



