6 U.S. NATIONAL MUSEUM BULLETIN 2 73 



Pars profunda has a fleshy origin from the lower hp and internal 

 surface of the zygomatic arch where, rostrally, the fibers are difficult 

 to separate from those of m. temporalis. A zygomaticomandibular 

 portion (see Starck, 1933) is not identifiable as a separate bundle. 

 This origin occupies in the jugal arch an extension equal to that of 

 the pars superficialis. Profunda fibers are entirely muscular in the 

 anterior three-fourths where they are almost vertical and attach 

 rapidly to the bone. Those of the posterior fourth are superficially 

 tendinous near the ramus but muscular elsewhere. They run down and 

 forward ending after a short course. Insertion of pars profunda is on 

 the upper fourth of the ramus and causes an excavation of the bone 

 below the incisura mandibulae. Between the attachment of the two 

 parts there is a wide area not occupied hj muscular insertion. A few 

 tendinous strands developed within the substance of the masseter, 

 especially where pars superficialis and profunda form a single mass, 

 fasten to the ramus together with the fleshy bundles. 



According to Leche (1912) the muscle is relatively thicker in the 

 embryo than in the adult howler and the space between its two parts 

 narrower. He concludes, therefore, that the enlargement of the 

 mandible, which takes place later, must be associated with other 

 factors besides growth of the masseter. Starck (1933) compared 

 the weights of this muscle and the temporalis in his specimens. He 

 obtained a ratio wt. temporalis/wt. masse ter= 1:1.23 in the juvenile, 

 1:1.07 in an adult female, and 1:0.9 in an adult male. This indicates 

 that even if the masseter enlarges with age and sex, its growth rate 

 is less than that of the temporalis. The masseter of Mycetes fuscus 

 (=Alouatta fusca) described by Sirena (1871) presents no significant 

 difference. 



Nerve supply : A branch of the anterior division of the mandibular 

 nerve. 



Function: Both parts are elevators of the mandible. Pars super- 

 ficialis and fibers from the anterior three-fourths of the profunda are 

 protractors, those of the posterior deep fourth retractors. 



M. pterygoideus lateralis: This two-bellied muscle is found between 

 the anterolateral surface of the medial pterygoid behind and the 

 terminal portion of m. temporalis in front (fig. 3). It is cone-shaped, 

 its base corresponding to the medial wall of the infratemporal fossa 

 and its apex to the processus condyloideus of the mandible. The 

 caput superior is smaller and weaker; its fleshy fibers arise from the 

 facies and crista infratemporalis of the alisphenoid. They pass latero- 

 dorsally in an almost horizontal plane to join those of the lower 

 head. The large caput inferior originates by equally fleshy bundles 

 from the lateral surface of the entire pterygoid plate and the per- 

 pendicular lamina of the palatine. The bundles also run dorsad but 



