CHAPTER XXV. 



Ungulates, — continued. 



The Pig-Like Ungulates. 



Family SU1D& 



The whole of the even-toed Ungulates described in the five preceding chapters are 

 characterised by their power of ruminating, with which is associated their crescent- 

 like, or selenodont, molar teeth (see figures on p. 155), and, with but one exception, 

 the presence of a cannon-bone in the limbs (see p. 154). We now come to more 



SKELETON OF WILD BOAH. 



generalised forms of the same great group of Ungulates, such as pigs and 

 hippopotami, which lack the power of rumination, and in which the structure of 

 the molar teeth and lower portion of the limbs is of different nature. 



At the present day there is a great gap between the types with 

 crescent-like molars and the pig-like animals ; a gap so wide that the 

 earlier naturalists failed to recognise the intimate relation that really exists between 

 the two. This gap is, however, almost completely bridged over by a number of 

 extinct Ungulates, and since, in order to have any adequate idea of the relations of 

 the existing groups, some knowledge of the fossil forms is absolutely essential, we 

 must devote a brief space to their consideration. 



First, with regard to the molar teeth. On p. 155 there is figured an upper 

 molar of a modern Ruminant, showing that the crown is surmounted by four 



