12 U.S. NATIONAL MUSEUM BULLETIN 2 73 



and lingula. The muscular bundles are continuations of the rather 

 short aponeurotic fascicles. Insertion is on the lateral surface of the 

 bulla along a line which follows the nonlingual border of the genio- 

 hyoideal area of attachment (fig. 3). Anterior fibers of the muscle 

 pass from one mylohyoid line to the other in front of the rostral end 

 of the bulla. Their continuity with the rest of the muscle is not very 

 clear and Sirena (1871) described them as a separate structure, 

 m. transversus maxillae inferioris. On the basis of their origin and 

 topographical relations I regard them as the anterior part of the 

 mylohyoideus which has been partially separated from the rest of 

 the muscle by the changes in the hyoid apparatus. I did not find 

 the continuity of the mylo- and geniohyoideus mentioned by Sirena 

 (1871). The two muscles are indeed very close to each other at the 

 rostral pole of the hyoid, but a space can be demonstrated in between. 

 Sandifort (1834) described the mylohyoideus as thin and embracing 

 the bulla. Bijvoet (1908) also found fibers of the muscle intercrossing 

 in the midhne. 



Nerve supply: The innervation of the muscle is by the mylohyoid 

 branch of the inferior alveolar nerve. 



Function: Elevation of the bulla. It also perhaps collaborates 

 with the geniohyoideus in pulling this bone forward. 



Comparative anatomy of the trigeminal group. — Starck (1933) 

 has already pointed out that among the platyrrhines he examined 

 Alouatta and Lagothrix stand out by themselves with respect to the 

 characteristics of their masticatory muscles. The development of the 

 hyolaryngeal apparatus in the first has influenced these structures 

 and most authors concerned agree on this point (Bijvoet, 1908; Leche, 

 1912; Starck, 1933). In addition to the overall differences in dimensions 

 it is perhaps those related to the insertion of the anterior digastric 

 belly which is more typical of the howler. The available literature 

 (Bijvoet, 1908; Leche, 1912; Starck, 1933) almost as a whole notes 

 this divergence, which is even more evident in the young individuals 

 (van den Broek, 1920; Starck, 1933). The distorted mylohyoideus is 

 also unique in this animal. Lagothrix is pecuUar in the orientation of 

 the single-beUied pterygoideus lateraUs; the muscle is frontally placed 

 in the infratemporal fossa (Starck, 1933). The differences in the 

 masticatory muscles between the capuchin, spider, and wooUy 

 monkeys are minor to the point that Starck (1933) grouped the first 

 two into a single class which did not include Lagothrix because of its 

 pecuUar lateral pterygoid. The muscles in Cebus appear to be pro- 

 portionately stronger than in the Atelinae and the fascicles of the 

 masseter reach the inner surface of the angle by turning around the 

 basis mandibulae (Starck, 1933). A zygomaticomandibular portion 

 was very strong in one of the capuchin specimens of Starck (1933), 



