PECO R A 



3" 



generally be distinguished, inasmuch as t be true molars of the ( '< rvidce 



are more or less brachydont, and those of the Bovidce generally 



hypsodont, i.e. the teeth of the former have 



comparatively short crowns (Fig. 122), which, 



as in most mammals, take their place at once 



with the neck (or point where the crown and 



root join) on a level with or a little ahove the 



alveolar border, ami remain in this position 



throughout the animal's life; whereas in the 



other forms (Fig. 123), the crown heing lengthened 



and the root small, the neck does not come up 



to the alveolar level until a considerable part ^JZ^SZ 



of the surface has worn away, and the crown of unsis, to show brachydont 



the tooth thus appears for the greater part of type. (From the Patacmfo- 



the animal's life partially buried in the socket. 0CJia 



In this form of tooth (which is almost always most developed 



in the posterior molars of the permanent series) the constituent 



columns of the crown are necessarily nearly parallel, whereas 



Fio. 122. — Crown sur- 



]•,,.. 123.— Inner and outer aspects of an almost unworn left upper molar of the Nilghai 

 (Boa ' "(locamelus), to show hypsodont type. (From the Pukeontologia Indica.) 



in the first-described they diverge from the neck towards the free 

 or grinding surface of the tooth. In the completely hypsodont 

 form the interstices of the lengthened columnar folds of enamel 

 and dentine are filled up with cement, which gives stability to 

 the whole organ, and is entirely or nearly wanting in the short- 

 crowned teeth. The same modification from low to high crowns 

 without essential alteration of pattern is seen in an even still 

 more marked manner in some of the Perissodactyle Ungulates, 

 the tooth of the Horse bearing to that of Anchitherium the same 

 relation as that of an Ox does to the early selenodont Artiodactyles. 



