x] PRIMATES. 143 



great development from the posterior border. It is generally 

 convex below, and concave above and behind, forming a 

 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 the former ; the Leniurina, on the other hand, more 

 resemble the lower type. 



In the Common Lemur the general proportions of face 

 to cerebral cavity, and the inclination of the occipital and 

 olfactory planes of the cranium, are quite dog-like. The 

 orbits, although completely surrounded behind by the 

 junction of the postorbital processes of the frontal and the 

 malar, are yet perfectly continuous with the temporal fossa 

 beneath this bony bar ; that extension inwards of the 

 frontal and malar to meet the alisphenoid, and thus form a 

 posterior external wall of the orbit, so characteristic of 

 Man and all Monkeys, being absent. The lachrymal fora- 

 men, situated on the facial part of the bone, is altogether 

 external to the margin of the orbit. The os planum of 

 the ethmo-turbinal does not enter into the inner wall of 

 the orbit, but is shut out from it by the maxilla, as in 

 most inferior mammals'. The inferior surface of the tym- 

 panic is developed into a large rounded bulla. The hyoid 

 apparatus much resembles that of the Dog, having the 

 stylohyal, epihyal, and ceratohyal all distinctly ossified in 



