PECORA 311 
generally be distinguished, inasmuch as the true molars of the Cerridi 
are more or less brachydont, and those of the Dovid generally 
hypsodont, ie. 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 above the 
alveolar border, and remain in this position 
throughout the animal’s life; whereas in the 
other forms (Fig. 123), the crown beinglengthened bs 
and the root small, the neck docs not come up — Fis. 122.—Crown sur. 
to the alveolar level until a considerable part a eee 
of the surface has worn away, and the crown of ensis,to shew brachydont 
the tooth thus appears for the greater part of type. (From the Patwonto- 
the animal's life partially buried in the socket. cuits 
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 neeessarily nearly parallel, whereas 
Pia. 128.—Inner and outer aspeets of an almost unworn left upper molar of the Nilghai 
(Roselaphus tragoviamelus), to show hypsodont type. (From the Paleontologia Indica.) 
in the first-deseribed 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 ave filled up with eement, which gives stability to 
the whole organ, and is entirely or nearly wanting in the short- 
crowned teeth. The same modifieation 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 -nchitheriun the same 
relation as that of an Ox does to the early selenodont Artiodactyles. 
