726 MAMMALIA [CH. 



having flat nails : the great toe or thumb or both are opposable 

 to the other digits. The orbits are rotated on to the anterior 

 aspect of the skull and are completely surrounded by bone 

 the brain is large. 



Sub-order 1. Lemuroidea. 



Primates in which the orbit is merely surrounded by a bony 

 ring : front teeth separated by a space in the middle line. 

 Ex. Lemur. 



Sub-order 2. Anthropoidea. 



Primates in which the orbit is completely separated from 

 the temporal fossa by an inwardly projecting sheet of bone : 

 front teeth in contact in the middle line. 



Section A. Platyrrhini. 



Anthropoidea with a broad intern asal septum, three pairs 

 of premolar teeth and a simple tympanic bone : the great toe 

 opposable to the other toes : the thumb imperfectly or not at 

 all opposable to the other fingers. 



Family 1. Hapalidae. 



Small thickly furred Platyrrhini with a flat nail on the 

 great toe only, claws on all the other digits : two molar 

 teeth on each side. 



Ex. Hapale, Midas. 



Family 2. Cebidae. 



Platyrrhini with flat or slightly curved nails on all toes : 

 three molar teeth on each side. 

 Ex. Ateles, Cebus. 



Section B. Catarrhini. 



Anthropoidea with a narrow internasal septum, two pairs 

 of premolar teeth and three pairs of molars in each jaw. 

 The tympanic bone has a tube-like prolongation. The great 

 toe is opposable to the other toes, the thumb imperfectly op- 

 posable to the other fingers. 



Family 1. Cercopithecidae, 



Catarrhini with arms not longer than their legs : bare 



