II MILK DENTITION 51 
teeth in which the grinding surface is raised into a series of two, 
to many, tubercles sharper or blunter as the case may be ;—sharper 
and fewer at the same time in carnivorous and especially in 
insectivorous types, more abundant in omnivorous animals. To 
this form of tooth the term “bunodont” is applied. There is 
no doubt that this is the earliest type of tooth; but whether the 
fewer or the more cusped condition is the primitive one is a 
question that is reserved for consideration at the end of the 
present chapter. The other type of grinding tooth is known as 
“Jophodont.” This is exemplified by such types as the Perisso- 
dactyla and Ungulates generally, and by the Rodents. The tooth 
is traversed by ridges which have generally a transverse direction 
to the long axis of the jaw in which the tooth lies. The ridges 
ph. 
H 
mh. 
Fic. 36.—Molar teeth of Aceratherium platycephalum. x4. m.1-m.3, Molars ; mh, meta- 
loph ; p.l-p.4, premolars; ph, protoloph ; ps.f, parastyle fossa ; fe, tetartocone. 
(After Osborn. ) 
may be regarded as having been developed between tubercles 
which they connect and whose distinctness as tubercles is 
thereby destroyed. Lophodont teeth are only found in vegetable- 
feeding animals. 
The special characteristics of the teeth of various groups of 
animals will be considered further under the accounts of the 
several orders of recent and fossil Mammalia. 
A very general feature of the teeth of the Mammalia is what 
is usually termed the diphyodont dentition. In the majority of 
vases there are two sets of teeth developed, of which the first 
lasts for a comparatively short time, and is termed on account of 
its usual time of appearance the “milk dentition”; this is 
replaced later by the permanent dentition. In lower vertebrates 
the teeth are replaced as worn away. There is not, however, 
so great an antithesis in this matter between the Mammalia 
