THE ANIMAL KINGDOM 457 



Order 16. Perissodactyla. Odd number of digits (five, three, or 



one) the axis of the foot passing through the middle of the third 



digit. 



Examples: Horse, zebra, tapir, and rhinoceros. 



Man. — The Primates, the order to which man belongs, are, from 

 the standpoint of general anatomy, the most primitive mammals 

 with the exception of the Insectivora, and for that reason occupy 

 a position among the lowest orders. When compared with 

 Primates, most other mammals show considerably more departure 

 from the original type, as for example, in the general form of the 

 body of the whale or manatee, the specialized fore arm of the bat 

 or the mole, the hoof of the ungulate, or the teeth of the rodent. 

 The primitive characters of the Primates are best seen in the 

 skeleton, which aside from the skull has retained the original 

 elements of the class with but little modification. Thus, in Man 

 the clavicle is present, both radius and ulna occur in the forearm 

 and the tibia and fibula in the leg; the arrangement of bones of 

 the wrist is primitive, the elements being distinct and showing 

 only slight modification. On the other hand, the ankle region is 

 modified as a result of the elongation of the foot which anatom- 

 ically is more highly specialized than the hand; the tail, highly 

 developed in some Primates, is absent in apes and Man, being 

 represented by the coccyx, composed of reduced caudal vertebrae 

 and not visible externally. 



The important feature which makes the Primates a superior 

 group is the brain and this reaches its highest development in 

 Man. The enlargement of the brain has been accompanied by 

 modifications in the cranium and secondary modifications in 

 the face, such as the forward-directed orbits, the reduction of the 

 nasal region with a corresponding loss of olfactory sense, the 

 shortening of the jaws and the retreat of the teeth, the latter 

 causing the formation of the chin in the lower jaw. Very likely 

 the shortening of the face developed as the hand with its opposa- 

 ble thumb came to be used more and more to bring food to the 

 mouth, thus relieving the latter of seeking and grasping food. 



Primates were, and some of them still are, essentially arboreal 

 animals. Man is a terrestrial animal, descended in all probability 

 from arboreal ancestors. The change from arboreal to terrestrial 

 habitat is thought for many reasons to have taken place in Cen- 

 tral or Southern Asia as a direct result of an increase in bulk too 



