THE RADIAL REGIOX. 



405 



Relations. By its superficial surface, with the Flexor longus pollicis and the 

 outer head of the Flexor brevis pollicis. Its deep surface is in relation with the 

 deep palmar arch, which passes between the two adductors. 



The Adductor transversus pollicis (Fig. 242) 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 part 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 inser- 

 tion a slip is prolonged to the Extensor longus pollicis. 



Relations. By its superficial surface, 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 

 aponeurosis. 



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

 and the Flexor brevis pollicis, at their insertions give off fibrous expansions which 



EXTENSOR LONGUS 

 POLLICIS. 



First metacarpal 

 bone. 



OPPONENS POLLICIS. 



FIG. 242. Muscles of thumb. (From a preparation in the Museum of the Royal College of Surgeons oi 

 England.) 



join the tendon of the Extensor longus pollicis. This permits of flexion of the 

 proximal phalanx and extension of the terminal phalanx at the same time. These 

 expansions, originally figured by Albinus, have been more recently described by 

 M. Duchenne (Phygiologie des Mouvements). 



Nerves. The Abductor, Opponens, and outer head of the Flexor brevis pollicis 

 are supplied by the sixth cervical through the median nerve; the inner head of the 

 Flexor brevis, and the Adductors, by the eighth cervical through the ulnar nerve. 



Actions. The actions of the muscles of the thumb are almost sufficiently indi- 

 cated by their names. This segment of the hand is provided with three extensors 

 an extensor of the metacarpal bone, an extensor of the first, and an extensor of 

 the second phalanx ; these occupy the dorsal surface of the forearm and hand. 



