TEETH 



137 



eight teeth in all including the tusks and a pair of evanescent incisors. 

 But of the six grinders not all are in use at one time. As the foremost 

 wears down and is shed, a second and larger moves into its place, only to 

 be followed by the remaining teeth in succession. Thus an old animal, 

 since there are no canines, may have only the two tusks and four grinders. 

 The grinders themselves are remarkable for their enormous size, the 

 largest being more than a foot from front to rear and four inches wide. 

 Each tooth is highly complex, with intricate folding of enamel and dentine, 

 so that as the softer dentine wears away faster, the tooth keeps always 

 its sharp grinding ridges. The same arrangement on a smaller scale 

 appears in various other vegetarian mammals, notably in the horse. The 



-PALATINE 



A. CAUCASIAN B. NEGRO C. ORANG OUTAN 



Fig. 125. — Dental arcades of ape, Negro and Caucasian. The fcjrm of the Negro 

 arcade is transitional between that of the ape and white man. With the shortening 

 of the human jaw the diastema between incisor and canine teeth seen in the ape jaw 

 is lacking. The refinement of the face is one of the most striking results of primate 

 evolution. (Redrawn after Wiedersheim.) 



huge single teeth coming successively into use are a device for prolonging 

 the life of the animal long after any set of teeth all functional at once 

 would wear away. Apparently, as a result, the elephants are among the 

 longest lived of mammals. 



Primates. The primates, except for their hands, feet, and brains, 

 are a somewhat unspecialized group, and their teeth, though reduced in 

 number to conform to the shortened jaws, are little differentiated and 

 the enamel is not folded. The dental formula for the Old World monkeys 

 is 2-1-2-3 ill both jaws. But the New World monkeys have another 

 premolar, and sometimes lack one of the three molars. It is a curious 

 fact, which no special creationist has attempted to explain, that man, 

 also an Old World primate, has exactly the dental formula of the others. 



The canines in monkeys are somewhat longer than the other teeth, 

 and in the male gorilla are much like those of the less specialized carnivores. 



