108 U.S. NATIONAL MUSEUM BULLETIN 2 73 



and palmaris longus below (fig. 27). Fibers from this origin are fleshy 

 superficially but tendinous where the muscle lies against the pronator 

 teres and the flexor profundus. This head forms a ventr odors ally 

 flattened mass which is muscular only in the proximal three-fourths 

 of the forearm, and it gives off a sUp to the radial head of the deep 

 flexor. Distally, it changes into three round tendons for the three 

 ulnar digits. (2) A caput profundum is totally covered by the super- 

 ficialis and Ues against the ventral aspect of the deep flexor. Its 

 fleshy fibers originate also from the anterior surface of the ulnar 

 epicondyle medially and below the caput superficiale (fig. 27). They 

 form a narrow and long muscle which, in all specimens except one 

 male, possesses an intermediate tendon at about the junction of the 

 upper and middle thirds of the antebrachium. Near the AVTist the 

 distal belly forms a tendon for digit II. The four tendons of the 

 superficialis pass below the flexor retinaculum above those of the 

 flexor profundus. The usual arrangement is for the superficialis tendon 

 to digits III and IV to be ventral to those to the second and fifth. 

 In the central compartment of the hand they are between the palmar 

 aponeurosis and the common tendinous structure of the profundus 

 tendons and are here contained Anthin tendomuscular tunnels formed 

 by (1) lumbricales at each side, (2) the profundus in a deep plane, 

 and (3) fine but resistant transverse fibrous connections between 

 each pair of lumbricals (fig. 33a). In the digits the tendons of the 

 superficialis travel beneath the vaginal flexor sheaths and over the 

 corresponding tendons of the j^rofundus. They divide at or a little 

 beyond the metacarpophalangeal joints into two bands which thus 

 leave an opening for the deep flexor tendon to pass through. The two 

 bands end on the lateral margins of the second phalanx. They are 

 joined by vincula longa to every first phalanx and by vincula brevia 

 to every second phalanx just before they end. 



Alouatta jusca has the same diAasion of the superficial fiexor (Sirena, 

 1871) as the red howler. The digastric deep head is called m. flexor 

 indicis subHmis proprius by Sirena (1871) on account of its individu- 

 ahty. Grand (1967) has found the same pattern in howlers from 

 northern Argentina, except that the contribution to the deep flexor 

 comes rather from the proximal head. 



Nerve supply: The median nerve provides separate branches for 

 each head of the muscle. 



Function: Flexor of the proximal interphalangeal articulation. 



M. palmaris longus: This muscle lies superficially between the 

 flexor carpi radialis and the flexor carpi ulnaris, in front of the flexor 

 digitorum superficialis. It arises from the lowest part of the tip of 

 the medial epicondyle, where its fibers and the epicondylar ones of 

 the flexor carpi ulnaris are very difficult to separate (fig. 27). The 



