82 U.S. NATIONAL MUSEUM BULLETIN 2 73 



and fleshy band whose insertion is by means of short tendinous fibers 

 on the upper fourth of the medial margin of the humerus or buttress 

 for the lesser tuberosity (fig. 27) . The buttress for the lesser tuberosity 

 and that for the humeral head remain separate in Alouatta, blending 

 distally with the surface of the shaft as in Ateles (Napier and Davis, 

 1959; Schon, 1965) and Cebus (Schon, 1964b). 



The muscle studied in Mycetes fuscus (= Alouatta fusca) by Sirena 

 (1871) is similar and, apparently, the findings of Campbell (1937) in 

 the Central American howler are also the same, as he does not stress 

 any different character. 



Nerve supply: The inferior subscapular nerve enters the muscle 

 and probably receives fibers from C V and VI (fig. 26). 



Function: A medial rotator and retractor of the humerus. It 

 helps to propel the animal by this latter mechanism. 



M. subscapularis (fig. 17): It is a powerful triangular muscle 

 occupying in the scapula the whole extent of its costal surface except 

 the marginal area along the vertebral edge and the neck (fig. 24). 

 The muscle is formed by several bipennate bundles whose fibers 

 originate from the three borders of the bone and from the surface of 

 the fossa, which is marked off by transversely oriented crests inter- 

 vening between broad grooves. Long but not very high tendinous 

 septa are implanted on these ridges and provide additional origin. 

 The pars axillaris of the subscapularis from the axillary sulcus is 

 prominent. All the fibers converge toward the scapulohumeral joint 

 in front of which they form a flattened tendon firmly connected to 

 the articular capsule and inserted on the lesser tubercle (fig. 27). 



Its arrsingement in Mycetes Juscus {= Alouatta fusca) (Sirena, 1871) 

 and Alouatta palliata (Campbell, 1937) is the same. 



Nerve supply: Several subscapular nerves, superior and inferior, 

 innervate the muscle. They all probably carry fibers from C V and 

 VI (fig. 26). 



Function: A strong medial rotator of the arm and stabilizer of 

 the shoulder joint. 



Figure 27. — Muscular attachments in the arm and forearm: a, Humerus (1, m. pectoralis 

 abdominalis; 2, m. subscapularis; 3, m. coracobrachialis, pars profunda; 4, m. latissimus 

 dorsi; 5, m. teres major; 6, m. coracobrachialis, pars media; 7, m. brachialis; 8, m. pronator 

 teres; 9, m. flexor carpi radialis; 10, m. flexor digitorum superficialis, caput profundum; 

 11, m. palmaris longus; 12, m. flexor carpi ulnaris; 13, m. flexor digitorum superficialis, 

 caput sperficiale; 14, m. flexor digitorum profundus, caput radiale; 15, m. extensor digiti 

 quinti et quarti proprius (= extensor digiti minimi of N.A.); 16, m. extensor digitorum; 

 17, mm. extensores carpi radialis brevis and longus; 18, m. brachioradialis; 19, m. del- 

 toideus; 20, m. teres minor; 21, m. infraspinatus; 22, m. supra spinatus); b, Radius and 

 ulna (1, m. epitrochleo-anconeus; 2, m. flexor carpi ulnaris; 3, m. flexor carpi radialis; 

 4, m. brachioradialis; 5, m. flexor digitorum profundus, caput radiale; 6, m. pronator 

 quadratus; 7, m. flexor digitorum profundus, caput ulnare; 8, m. biceps brachii; 9, m. 

 pronator teres; 10, m. supinator; 11, m. brachialis. 



