CHAPTER XV 



HISTORY OF THE PRIMATES 



This order embraces the lemurs, monkeys, man-like apes 

 and Man, though in the general account Man will be omitted 

 from consideration. The Primates are clothed in dense fur 

 or shaggy hair. The teeth are always low-crowned and rooted 

 and reduced in number, the incisors generally to | and the 

 premolars to |-| ; the molars are trituberculate or quadri- 

 tuberculate. The cranium is unusually capacious and the 

 orbit is entirely encircled in bone. The tail varies much in 

 length and may be entirely wanting. The bones of the fore- 

 arm and lower leg are separate and the radius has much freedom 

 of rotation, in correspondence with the grasping power of 

 the hand. The pes is also a grasping organ and, with few 

 exceptions, the thumb and great toe are opposable to the other 

 digits ; the bones of the wrist do not coossify and frequently 

 the central is present. The feet are plantigrade and almost 

 always pentadactyl and, with a few exceptions, have neither 

 claws nor hoofs, but flat nails ; the ungual phalanges are 

 correspondingly modified and do not taper toward the free 

 end, but expand at the tip. The Primates are characteristically 

 arboreal in habit, but a few, such as the baboons, have become 

 secondarily adapted to a terrestrial mode of life. They inhabit 

 at present all the tropical regions of both hemispheres, Aus- 

 tralia excepted. Extratropical North America has no existing 

 member of the order and, so far as we know, has had none since 

 the Eocene epoch. The most important of the genera of the 

 western hemisphere are listed below. 



2p 577 



