462 



MYOLOGY 



The Adductor pollicis (obliquus) (Adductor obliquus pollicis) arises by several 

 slips from the capitate bone, the bases of the second and third metacarpals, the 

 intercarpal ligaments, and the sheath of the tendon of the Flexor carpi radialis. 

 From this origin the greater number of fibers pass obliquely downward and con- 

 verge to a tendon, which, uniting with the tendons of the medial portion of the 

 Flexor pollicis brevis and the transverse part of the Adductor, is inserted into 

 the ulnar side of the base of the first phalanx of the thumb, a sesamoid bone 

 being present in the tendon. A considerable fasciculus, however, passes more 

 obliquely beneath the tendon of the Flexor pollicis longus to join the lateral portion 

 of the Flexor brevis and the Abductor pollicis brevis. 



I 





Pisometacarpal lig. 



Fia. 426. The muscles of the thumb. 



The Adductor pollicis (trans versus) (Adductor tr answer sus pollicis) (Fig. 426) 

 is the most deeply seated of this group of muscles. It is of a triangular form 

 arising by a broad base from the lower two-thirds of the volar surface of the 

 third metacarpal bone; the fibers converge, to be inserted with the medial part of 

 the Flexor pollicis brevis and the Adductor pollicis (obliquus) into the ulnar side 

 of the base of the first phalanx of the thumb. 



Variations. The Abductor pollicis brevis is often divided into an outer and an inner part; 

 accessory slips from the tendon of the Abductor pollicis longus or Palmaris longus, more rarely 

 from the Extensor carpi radialis longus, from the styloid process or Opponens pollicis or from the 

 skin over the thenar eminence. The deep head of the Flexor pollicis brevis may be absent or 

 enlarged. The two adductors vary in their relative extent and in the closeness of their connection. 

 The Adductor obliquus may receive a slip from the transverse metacarpal ligament. 



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

 supplied by the sixth and seventh cervical nerves through the median nerve; the medial head 

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



Actions. The Abductor pollicis brevis draws the thumb forward in a plane at right angles 

 to that of the palm of the hand. The Adductor pollicis is the opponent of this muscle, and approxi- 

 mates the thumb to the palm. The Opponens pollicis flexes the metacarpal bone, i. e., draws 

 it medialward over the palm; the Flexor pollicis brevis flexes and adducts the proximal phalanx. 



2. The Medial Volar Muscles (Figs. 426, 427). 

 Palmaris brevis. Flexor digiti quinti brevis; 



Abductor digiti quinti. 



Opponens digiti quinti. 



