The Evolution of the Ilurse. 
123 
sets, called (beginning from the front) incisors, canines, 'pre- 
molars, and molars; and all the early Ungulate animals had, 
without exception, on each side, above and below, three incisors, 
one canine, four premolars, and three molars — that is, eleven on 
each side above and eleven below, or forty-four altogether. The 
modern horse has very nearly, but not quite, this full number. 
The front teeth, or incisors, are the same, taking the two sides 
together, six above and six below. The canines or " tushes," are 
present, as a rule, only in the males. The cheek-teeth, or 
molars and premolars, taken together (for there is very little to 
distinguish them in form or size), are generally but six, instead 
of seven. Here, then, is a case of specialisation by suppression. 
One of the teeth of the ancient forms has disappeared. Which 
is it? The examination of fossil remains shows us that the 
first of the series — the anterior premolar, a fairly large and well- 
developed tooth in Phenacodus and Hyracotherium — gradually 
became smaller and smaller as time advanced. But has it 
entirely disappeared in the modern horse ? AVhat do we read 
in old books on veterinary surgery ? — " Wolves' teeth are two 
very small, supplementary teeth, appearing in front of the molar 
teeth, and supposed to have an injurious effect on the eyes (!), and 
are therefore often removed by farriers. 1 ' These little rudiments 
of teeth, about which such nonsense as the above has been 
written, are, when properly understood, of intense interest. 
Their diminutive size, their irregular form and inconstant 
presence, combined with their history in the extinct horse-like 
animals, show them to be teeth which, for some reason to us at 
present unknown, have become superfluous — have been very 
gradually and slowly (as in the case of all operations of the 
kind) dispensed with, and are, in the stage to which the horse 
has now arrived in its evolution, upon the point of disappearance. 
The presence of these so-called " wolves' teeth " alone is suf- 
ficient, if we had no other proof, to show that the horse is not an 
isolated creation, but one link in a great chain of organic beings. 
The six remaining molar teeth (or, rather, three premolars 
and three true molars) have undergone a remarkable series of 
modifications as time advanced. The crowns of all these teeth 
in the early forms were very short ; there was a distinct con- 
striction — the neck — between the crown and the roots, and when 
the teeth were developing, as soon as the neck once rose fairly 
above the alveolar margin, the tooth remained permanently in 
this position. The term " brachydont," or short tooth, ex- 
presses this condition. The free surface had two, nearly trans- 
verse, curved ridges, with valleys between, and had no deposit 
of cementum filling them, the whole exposed surface of the 
