MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 19 



moval of the last two. (2) Fibers of the intermediate layer arise from 

 the outer edge of the maxiUary alveolar border and the ill-defined 

 pterygomandibular raphe. Running almost horizontally forward they 

 end deep to the orbicularis intermixing with other buccinator fibers 

 at the angulus oris. (3) The deeper stratum can be seen between the 

 mandible and the lower margin of layer (2). Origin is from the said 

 raphe, the lower part of the temporal crest of the mandible, and the 

 external border of the alveolar process. Its fibers run obUquely toward 

 the corner of the mouth at an angle to those of the previous layer. 

 They have a similar ending. I could not demonstrate a double layering 

 of fibers in layer (3) as claimed by Schreiber (1928). The whole muscle 

 is separated from the overlying ones by the clumps of an extensive 

 facial fatty pad. Sirena (1871) and van den Broek (1920) describe, 

 in no very clear details, a paired m. mentalis. I think that both might 

 have been confused by the deep fibers of the platysma inserted on the 

 juga alveolaria. Schreiber (1928) does not include the mentalis in his 

 account of the howler, but adds when discussing this muscle among 

 the platyrrhines that the condition in the hapalids (=callithricids), 

 that is, the presence of a mentahs, is a character common to the other 

 species he studied. I could not demonstrate this muscle. 



Nerve supply: All the derivatives of the sphincter colli profundus 

 are suppHed by branches of the preauricular rami of the facial nerve. 



Comparative ANATOMY OF THE facial musculature. — Huber (1930) 

 regarded as progressive the common features of the facial musculature 

 which are found in the howHng, spider, and woolly monkeys. These 

 characters have also been observed by other authors in Ateles (HiU, 

 1962; Schreiber, 1928), Brachyteles (Hill, 1962), and Lagothrix (Hill, 

 1962; Schreiber, 1928). 



Cebus contrasts Avith the Atelinae and Alouatta in possessing a less 

 differentiated platysma and clear remains of an m. sphincter colli 

 profundus. The platysma colli et faciei in this genus arises from the 

 nuchal Hgament where it is partially covered by the suboccipital 

 origin of m. auricularis posterior and the occipitaUs (Schon, 1964b). 

 It has no insertion on the basis mandibulae and no connection with 

 the zygomatico-orbital plate (Ruge, 1887 ; Schreiber, 1928). A variably 

 developed m. sphincter colli profundus was observed by Schreiber 

 (1928) in three adult males, one Cebus macrocephalus ( = Cebus apella), 

 one Cebus capucinus, and one Cebus variegatus (=^ Cebus apella). I saw 

 this muscle in one adult male Cebus nigrivittatus. M. triangularis 

 appears as a derivative of the orbicularis oris because the caninus is 

 small (Schreiber, 1928). 



The platysma colli et faciei of Alouatta differs from that of Ateles 

 and Lagothrix in the fact that it is more extensive over the face where 

 it forms a continuous sheet with the zygomatic-orbital plate. The 



