MUSCULAR SYSTEM OF THE RED HOWLING MONKEY 31 



whole organ forward. The muscle must therefore be of importance 

 in the action of sticking the tongue out as in the premating behavior 

 of females (see Carpenter, 1934). It also probably plays a role in 

 opening the thyrohyoid canal (Schon, 1964a). 



M. hyoglossus: It is a large and well developed muscle extended 

 from the cornu branchiale I and the hyoid to the sides of the tongue 

 (fig. 3). Its fleshy bundles originate from the whole length of the said 

 cornu, the capsule of the hyoid-cornual articulation and the tentorial 

 and subtentorial surfaces of the bulla. Cornual fibers appear to be 

 continuations of those of m. thyrohyoideus across the surface of the 

 large hyoid horn. Hyoglossal fascicles at first are almost horizontally 

 directed toward the tongue, becoming increasingly less obHque until 

 those of bullar origin ascend rather vertically. On reaching the tongue 

 some cornual fibers pass between the genioglossus and the tentorium 

 to meet a similar group from the opposite side as described elsewhere 

 (Schon, 1964a) ; the rest intercross with the intrinsic hngual muscles 

 after covering the lateral aspect of the genioglossus. A similar muscle 

 was also found by both Sandifort (1834) and Sirena (1871). 



Nerve supply: N. hypoglossus. 



Function : Retractor of the tongue. 



M. styloglossus: This is a variable structure. It was present in 

 three of my males and I reported this finding earlier (Schon, 1964a), 

 but it was absent in another male and a female subsequently studied. 

 Only a fine tendinous structure not easy to isolate from the stylo- 

 mandibular ligament and parotid fascia represents the styloglossus 

 in these two specimens. It leaves the proximal end of the stylopharyn- 

 geus and running between the two styloid muscles ends on the lateral 

 side of the superior constrictor. Lampert (1926) did not find the 

 styloglossus in his two adult males. Sirena (1871) declares it to be 

 present and so does Sandifort (1834). Typically, the muscle leaves 

 the inner border of the stylohyoideus tendon and proceeds distally 

 to reach the pars linguahs of the superior pharyngeal constrictor. 



Nerve supply: N. hypoglossus. 



Function : Pulhng back the tongue. ' 



No information is given about the intrinsic muscles of the tongue 

 because they could not be well revealed by dissection. 



Comparative anatomy of the lingual group.— This group of 

 muscles was studied by Houpert (1927) in Ajteles, and Lampert 

 (1926), who observed them in the spider, woolly, and ring-tailed 

 monkeys. Their findings in general indicate attachments and relations 

 similar to those of the howler, but an evident lesser development, 

 most manifest in the hyoglossus. Lampert (1926) saw continuation 

 of the thyrohoideus and hyoglossus fibers in Cebus but not in Ateles. 

 Houpert (1927), on the other hand, does describe such an uninter- 



