MUSCLES OF THE THOR/iClC LIMBS. 185 



M. adductor pollicis (Fig. 89, b). 



Origin by fleshy fibres fi-om the ventral border of the os 

 magnum. It curves about the base of the first metacarpal on 

 its ulnar side to its insertion. 



Insertion by fleshy fibres into the base of the first j^halanx 

 of the pollex on its ulnar side. 



C. Muscles Lying between the Metacarpals. — 

 Mm. interossei (Fig. 89). — Small stout muscles lying on the 

 palmar surfaces of the metacarpals of the second, third, fourth, 

 and fifth digits. 



Origin by fleshy fibres from the ventral or lateral surfaces 

 of the bases of the metacarpals. Near the distal end of the 

 metacarpal each divides into two masses which pass onto the 

 lateral surfaces of the metacarpal, so as to leave the ventral 

 surface of the distal end exposed. 



Insertion partly onto the lateral surfaces of the base of the 

 first phalanx and its sesamoids, and partly by a slender tendon 

 (Fig. 84, h) which is continued dorsad to join the extensor 

 tendon of the digit. 



D. Special Muscles of the Second Digit (the 

 Index). — M. flexor brevis digiti secundi (or indicis). — This 

 name may be applied to M. interosseus of the second digit 

 (Fig. 89, c). 



M. abductor digiti secundi. — This name might be applied 

 to a portion of the interosseus of the second digit which is 

 sometimes differentiated from the remainder. 



Origin from the radial and ventral surfaces of the base of 

 the second metacarpal, and from the ventral surface of the 

 trapezium. 



Insertion into the radial side of the base of the first phalanx 

 of the second digit and into its sesamoid. 



M. adductor digiti secundi (Fig. 89, d). 



Origin from the ventral surface of the os magnum. 



Insertion into the ulnar side of the base of the first phalanx 

 of the second digit. 



E. Special Muscles of the Fifth Digit. — M. ab- 

 ductor digiti quinti (Fig. 89, i). — A thick, small, conical 

 bundle. 



