MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 59 



Sirena (1871) claims that all of these four paired muscles in the 

 howler are as in man. 



Nerve supply of the cervical subvertebral muscles. — They 

 all receive small twigs from the anterior divisions of the cervical 

 nerves. M. rectus capitis anterior and the lateralis are innervated 

 in particular by the anterior division of C I. 



Function of the cervical subvertebral muscles. — They flex 

 the head and neck, both ventrally and laterally. 



Comparative anatomy of the cervical subvertebral 

 muscles. — Hill (1962) covers both mm. longus capitis and colli in 

 the woolly spider monkey. The first muscle is said by him to arise from 

 the transverse processes of C 5 to 7, the second to be formed by the 

 usual three portions. Forster (1916a) studied these two muscles in 

 Ateles where the capitis is assigned an origin from C 3 to 6 and the 

 longus atlantis (pars obliqua superioris musculi longus colli) is said 

 to extend from the costal component of C 3 to the atlas. 



M. qiiadratus lumhorum (fig. 20): It is a ventrally compressed 

 muscular column extending along the sides of the lumbar spine from 

 the last thoracic vertebrae to the iliac crest. The muscle is formed 

 initially by fleshy fibers coming from the disk between the two caudal 

 thoracic vertebrae and the body of the last one. The descending belly 

 Ues in front of the costal processes from which it receives on its dorsal 

 surface a series of tendomuscular digitations. It is separated from the 

 bodies of lumbar vertebrae 3 to 5 or 6 by m. psoas major. The prox- 

 imal fibers of the abdominal surface of the muscle end on the tip of 

 the first two costal apophyses, the rest are attached on the iliolumbar 

 ligament and the already described spine of the iliac crest. Insertion 

 also takes place on the last three or four costal processes by fleshy 

 slips from the dorsal surface of the quadratus. 



The muscle described by Sirena (1871) in Mycetes fuscus (=Alouatta 

 Jusca) is similar to that of the red howler monkey. He includes also 

 the last two ribs in the origin. 



Nerve supply: Branches from the ventral rami of L I, II, and III. 



Function: Lateral flexor of the lumbar spine. 



Comparative anatomy: The quadratus lumborum of Brachyteles 

 is described by Hill (1962) as bilaminar, with origins from the last 

 rib and all costal processes (ventral lamina) or only from that rib 

 (deep lamina). Insertion takes place on the iliac crest at its medial 

 part. 



Perineal Group 



As in the rhesus macaque (Howell and Straus, 1933), the perineal 

 muscles of Alouatta show a clear sexual dimorphism. They will be 

 described separately. 



275-199 O - 68 - 5 



