THE TEETH OF MAMMALS 159 



tern of the arrangement of the tissues of the 

 molars that is exact and constant. 



In the Artiodactyla, — the even-toed Ungulates, 

 — the first and most important group is that of 

 the Ruminants, — those herbivora which regurgi- 

 tate the bolus of food from the stomach to subject 

 it to a second chewing or rumination. This divi- 

 sion includes the Ox, Sheep, Deer, Antelope, 

 Giraffe, and indeed the greater part of the Artio* 

 dactyla, which have no incisors in the upper jaw. 

 The formula is usually, — 



. 0-0 0-0 3-3 3-3 on 



l. c. p.m. m. — = 30. 



3_3 o-0 p 3-3 3-3 



There are no incisors nor canines in the upper 

 jaw, but instead a hard pad of cartilage covered 

 with dense gum-tissue, against which the lower 

 incisors and incisor-like canines close in cutting 

 off grass. Eudimentary incisors are met with in 

 the Eed-deer, and the Musk-deer, Water-deer, and 

 Muntjac have formidable upper canines project- 

 ing downward below the lower jaw for weapons 

 and digging roots. The canines bear a more or 

 less distinct inverse relationship to the presence 

 or absence of horns, — i.e., when the upper canines 

 are present the horns are absent, or vice versa. 

 The molar teeth of this group present great vari- 

 ety as to the pattern of the grinding surface, but 

 within families are much alike. Thus the molars 

 of the ox family, the deer family, etc., have each a 



