2/0 COMPARATIVE ZOOLOGY, 



In the majority of mammals, the teeth are limited in 

 number and definite in their forms. The number ranges 

 from i in the narwhal (but the longest tooth in the 

 animal kingdom) to 220 in the dolphin. The average is 

 32, occurring in ruminants, apes, and man ; but 44 (as 

 in the hog and mole) is called the typical or normal 

 nutrfber, and this number is exceeded only in the lower 



FIG. 232. Skull of the Babirusa, or Malayan Hog, showing growth and curvature of the 



canines. 



groups. When very numerous, the teeth are of the 

 reptilian type, small, pointed, and of nearly equal size, 

 as in the porpoise. In the higher mammals, the teeth 

 are comparatively few, and differ so much in size, shape, 

 and use, that they can be classed into incisors, canines, 

 premolars, and molars. Such a dental series exhibits 

 a double purpose, prehension and mastication. The 



