116 U.S. NATIONAL MUSEUM BULLETIN 2 73 



M. abductor digiti quinti (=abductor digiti minimi oj N.A.): This 

 is a well-developed muscle when compared to the small, short pollical 

 abductor and is found on the ulnar and superficial aspect of the 

 hypothenar eminence (figs. 32, 33, 34). It takes a firm origin on the 

 distal surface of the ventrally projecting pisiform, while many of 

 its superficial fibers come directly from the overlying skin. The muscle 

 runs over the palmar aspect of the very strong pisohamate and 

 pisometacarpal ligaments to which it is bound by the surrounding 

 connective tissue. At the level of the carpometacarpal articulation 

 a round tendon is formed and continues distally along the ulnar side 

 of the fifth metacarpal, finally reaches the ulnar tubercle of the meta- 

 carpal head where it ends. The insertion, according to Sirena (1871), 

 is on the ulnar base of the first phalanx. 



Nerve supply: The superficial branch of the ulnar nerve. 



Function: It abducts and flexes the fifth metacarpal. 



M. flexor digiti quinti {—flexor digiti minimi brevis of N.A.): This 

 is also superficial in the hypothenar side and lies along the radial 

 margin of the abductor of the fifth digit (figs. 32, 33, 34). Strong 

 and flat, it arises from the distal border of the flexor retinaculum. 

 Its fibers run distomedially, covering the opponens of the fifth digit. 

 They are inserted on the ulnar side and ulnar half of the palmar base 

 of the proximal phalanx. Sirena (1871) considers this muscle of the 

 howler to be just as in man. 



Nerve supply: A branch of the deep ulnar nerve. 



Function: A flexor of the fifth metacarpophalangeal joint. Due 

 to its insertion on the ulnar side of the phalanx, contraction of the 

 muscle would rotate the finger toward the axis of the hand. 



SUPERFICIAL SERIES, DEEP LAYER 



Mm. lumbricales: These are four long, cyhndrical muscles which 

 from their origins between the perforating tendons pass distally in 

 the middle compartment of the hand to end on the radial sides of 

 digits II to V (fig. 33a). The first lumbrical arises from the adjacent 

 sides of the tendons for digits I and II, the second between those 

 for II and III, the third between those for III and IV, and the fifth 

 from those for IV and V. Each lumbrical reaches the radial side of 

 the metacarpophalangeal joint where it crosses the palmar aspect 

 of the deep transverse ligament of the hand. The muscle now changes 

 into an aponeurotic and resistant membrane which blends distally 

 with the corresponding dorsal extensor expansion at about the proxi- 

 mal half of the first phalanx. 



Nerve supply: The first lumbrical is innervated by a branch from 

 the median nerve ramus to the radial side of the index. The second 

 lumbrical is also supplied by the median nerve, but through its ramus 



