MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 7 



with increasingly cranial inclination as their origin becomes more 

 caudal. The muscle narrows toward its insertion on the fovea ptery- 

 goidea of the condyloid process (fig. 2) and the capsule of the tem- 

 poromandibular joint. Through the last attachment it is also anchored 

 to the meniscus. The buccal nerve and associated vessels pass forward 

 between both heads. They enter the cheek region after traveling 

 between the lateral pterygoid and temporalis. The observations of 

 Sirena (1871) and Starck (1933) on the same muscle of the howler 

 call for no special comment. 



Nerve supply: The buccal nerve innervates the muscle when 

 passing between its two heads. 



Function : Protractor of the mandible. 



M. pterygoideus medialis: This large muscle is shaped like a 

 frontally compressed cone whose truncated apex corresponds to the 

 pterygoid origin and its base to the ending on the inner surface of the 

 angle and ramus of the mandible (figs. 3, 4). Origin (fig. 5) is (1) by 



(jo) ® ®© ® 



Figure 3. — Infra- and Suprahyoid muscles. Some masticatory muscles (1, m. costothy- 

 roideus; 2, m. sternothyroideus; 3, m. cricothyroideus, pars obliqua; 4, m. cricothyroideus, 

 pars recta; 5, m. thyrohyoideus; 6, m. sternohyoideus; 7, m. stylohyoideus; 8, m. hyo- 

 glossus; 9, m. pterygoideus medialis; 10, m. mylohyoideus; 11, anterior fibers of the 

 mylohyoideus crossing in front of the bulla; 12, genial muscles arising below the torus; 

 13, m. pterygoideus lateralis; 14, m. digastricus, venter posterior). 



