X.] 



PRIMATES. 



165 



ossification in the anterior hyoid arch (see Fig. 54) ; but in 

 some Cercopitheci a short, bony, cerato-hyal is found. This 

 occurs also in the American Monkeys (Fig. 55), with occa- 

 sionally the addition of a second piece (epihyal). 



The thyrohyals are always well-developed, long, narrow, 

 nearly straight, and somewhat flattened. 



The basihyal varies much in form. In the anthropoid Apes 

 it is broad transversely ; but in nearly all the other Monkeys 

 its antero-posterior extent exceeds its breadth, owing to a 

 great development from the posterior border. It is generally 

 convex below, and concave above and behind, forming a 



FlG. 54. Inferior surface of hyoid boots 

 of Baboon (CyniKepkalm pamirim,), 

 bh basihyal ; th thyrohyal. 



FIG. 55. Inferior surface of hyoid bones 

 of an American Monkey (Lago'hruc 

 humbolJtii). tk thyrohyal ; c h cerato- 

 hyal ; ck epihyal. 



considerable cavity in which the median laryngeal air-sac 

 is lodged. This condition is enormously exaggerated in 

 the American Howling Monkey (Mycetes), where the basi- 

 hyal is transformed into an immense subglobular, thin- 

 walled, bony capsule, with a large orifice posteriorly, by 

 which the laryngeal air-sac enters, and having the straight 

 narrow thyrohyals attached on each side. In this genus 

 there are no ossifications in the anterior arch. 



While in nearly all the characters in which the skull of 

 Man differs from that of the Dog, the Simiina agree with 



