THE HEAD AND NECK. 115 



ing the two sides together (Fig. 16, i\ f-, and i 3 ). The 

 canines, or " tushes " (c), are present, as a rule, only 

 in the males. The cheek-teeth (pm 2 to w 3 ), or pre- 

 molars and molars taken together (for there is very 

 little to distinguish them in form or size), are gener- 

 ally but six, instead of seven, on each side above 

 and below. Here, then, is a case of specialization by 

 suppression. One of the teeth of the ancient forms 

 has disappeared. Which is it? The examination 

 of a series of fossil remains shows us that the first 

 of the series the anterior premolar (pm l ), a fairly 

 large and well-developed tooth in Phenacodus 

 and Hyracotherium gradually became smaller and 

 smaller as time advanced. It is still present in An- 

 chitherium, sometimes present and sometimes absent 

 in Hipparion. But has it entirely disappeared in the 

 modern horse f What 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." 



These little rudiments of teeth, about which such 

 nonsense as the above has been written, are, when 

 properly understood, of intense interest. Their di- 

 minutive size, their irregular form and inconstant 

 presence, combined with their history in the extinct 



