MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 13 



who also points out that the development of a strong temporaUs 

 contributes to the occasional formation of a sagittal crest in Cehus. 

 The pterygoideus lateralis oi Ateles (Starck, 1933) appears to be small. 

 All these muscles in Brachyteles (Hill, 1962) have a strong resemblance 

 to those of the spider monkey. Hill (1962) claims the presence of a 

 zygomaticomandibularis in the wooUy spider monkey. 



Facial Group 



Huber (1930, 1931, 1933) classified the muscles in the field of m. 

 faciahs into a superficial and a deep group. The first comprises all the 

 muscles discussed under facial musculature; the second includes the 

 stylohyoideus, posterior digastric belly, and the stapedius muscle. 

 The little muscle to the stapes was not exposed in my dissections, and 

 the whole of the digastricus was studied with the masticatory muscles 

 for functional reasons. 



Facial Musculature 



The facial musculature of some representative ceboids was the 

 object of an excellent study by Schreiber (1928). He examined four 

 specimens of Alouatta auratus (=Alouatta seniculus), two adult males, 

 one adult female, and one infantile whose sex was not specified. My 

 investigation corroborates and in some aspects complements his 

 findings for this genus. Van den Broek (1920) describes some of these 

 muscles in a young Mycetes (= Alouatta sp.) with full mUk dentition. 

 Huber (1930) refers to some of the intrinsic ear muscles in the Central 

 American species Alouatta palliata. Ruge (1887) does not say how 

 many specimens of Mycetes {=Alouatta sp.) he used, but his results 

 are largely confirmed by Schreiber (1928). Sirena's account (1871) 

 uses a different nomenclature but his material is comparable ^\■ith 

 those of other authors and my own. He gives no information about the 

 intrinsic ear muscles. 



Material for this section Avas obtained from four specimens. The 

 whole facial musculature could be studied in but two males ; the other 

 male and the female provided partial information. 



M. platysma colli et faciei: This is a well developed but thin mus- 

 cular sheet which covers the posterior and most of the anterior cervical 

 triangles, the parotideomasseteric, and part of the buccal and mental 

 regions (fig. 6). Its fleshy fibers arise freely in the superficial fascia of 

 the neck along a line that follows first the clavicle and then, up toward 

 the ear, the dorsal border of the posterior cervical triangle. Some fibers 

 override mm. trapezius and the atlantoscapularis anterior extending 

 dorsally for a very short distance but never all the way to the back of 

 the neck. Only Hill (1962) describes the origin of the muscle as almost 

 reaching the dorsal midhne in the nape, an observation which I regard 

 as his own because it is not found in any of the authors on whose 



