164 COMPARATIVE DENTAL ANATOMY 



The Peris sodactyla are much less numerous as 

 regards their living representatives, although 

 great numbers have lived on the earth in past 

 geological times. It includes the Horse, Rhinoc- 

 eros, Tapir, and their allies. The Horse family 

 has the formula, — 



. 3-3 1-1 4-4 3-3 AA 



L ^3 C - n p - m - S m ' 3^3 = **• 



The incisors are broad, thick, and slightly curved, 

 with a valley dipping down into the crown which 



Fig. 69. — Teeth of Horse {Equus caballus). 



when worn produces the well-known mark by 

 which the age of a horse is estimated (Fig. 69). 

 The canines are long and cubical in the male, but 

 smaller in the female. A considerable space ex- 

 ists between the canine and the premolars. The 

 first premolar is rudimentary, and often becomes 

 a source of irritation. It is popularly called the 

 "wolf-tooth," and is soon shed. The other pre- 

 molars are often as large and complex in pattern 



