THE RADIAL REGION. 493 



face, with the tendon of the Flexor carpi radialis : by its external surface, with the 

 Opponens pollicis: by its internal *i.irfa<-<-. with the Adductor obliquus pollicis. 



The Adductor obliquus poliicis arises by several slips from the os magnum, the 

 bases of the second and third metacarpal bones, the anterior annular ligament, and 

 the sheath of the tendon of the Flexor carpi radialis. From this origin the greater 

 number of fibres pass obliquely downward and converge to a tendon, which, 

 uniting with the tendons of the deeper portion of the Flexor brevis pollicis and 

 the Adductor transversus, is inserted into the inner side of the base of the first 

 phalanx of the thumb, a sesamoid bone being developed in the tendon of insertion. 

 A considerable fasciculus, however, passes more obliquely outward beneath the 



3d Metacarpal bone. 



FLEXOR BREVIS POLLICIS. 



/ 



ABDUCTOR POLLICIS. 



FIG. 315. Muscles of thumb. (From a preparation in the Museum of the Royal College of Surgeons of 

 England.! 



tendon of the long flexor to join the superficial portion of the short flexor and the 

 Abductor pollicis. 1 



Eelations. By its superiii'-tal surface, with the Flexor longus pollicis and the 

 outer head of the Flexor brevis pollicis. Its deep surface covers the Adductor 

 transversus pollicis. and is in relation with the deep palmar arch, which p.: 

 between the two adductors. 



The Adductor transversus pollicis (Fig. 315) is the most deeply seated of this 

 group of muscles. It is of a triangular form, arising, by its broad base, from the 

 lower two-thirds of the metacarpal bone of the middle finger on its palmar surface : 

 the fibres, proceeding outward, converge, to be inserted, with the inner tendon of 

 the Flexor brevis pollicis. and the Adductor obliquus pollicis, into the ulnar side of 

 the base of the first phalanx of the thumb. From the common tendon of insertion 

 a slip is prolonged to the Extensor longus pollicis. 



Eelations. By its *ni>erii'-!'il *-u.rface. with the Adductor obliquus pollicis. 

 the tendons of the Flexor profundus. and the Lumbricales. Its deep surface 

 covers the first two interosseous spaces, from which it is separated by a strong 

 aponeuri-- & 



Three of these muscles of the thumb, the Abductor, the Adductor transversus, 



1 This muscle was formerij described as the deep portion of the Flexor brevis pollicis. 



