432 



ORDERS OF MAMMALIA. 



to form a single bone, known as the " canon-bone." The 

 stomach is complex, and is divided into several compartments, 

 this being in accordance with their mode of eating. They all, 

 namely, ruminate or " chew the cud " that is to say, they first 

 swallow their food in an unmasticated or partially-masticated 

 condition, and then bring it up again, after a longer or shorter 

 time, in order to chew it thoroughly. 



The dentition of the Ruminants presents peculiarities almost 

 as great and as distinctive as those to be derived from the di- 

 gestive system. In the typical Ruminants (e.g., Oxen, Sheep, 

 Antelopes), there are no incisor teeth in the upper jaw, their 

 place being taken by a callous pad of hardened gum, against 

 which the lower incisors impinge (fig. 355). There are also no 



m 



Fig. 355. Skull of a hornless Sheep (after Owen), i Incisors; c Canines ; 

 in Molars and prjemolars. 



upper canine teeth, and the only teeth in the upper jaw are six 

 molars on each side. In the front of the lower jaw is a con- 

 tinuous and uninterrupted series of eight teeth, of which the 

 central six are incisors, and the two outer ones are regarded by 

 Owen as being canines. Upon this view, canine teeth are pre- 

 sent in the lower jaw of the typical Ruminants, and they are 

 only remarkable for being placed in the same series as the in- 

 cisors, which they altogether resemble in shape, size, and direc- 

 tion. Behind this continuous series of eight teeth in the lower 

 jaw there is a vacant space, which is followed behind by six 

 molars on each side. 



