320 A MANUAL OF DENTAL ANATOMY, 



ungulate which ever lived, there would be no doubt as to 

 the relationship of the various patterns : as it is, we are em- 

 barrassed by the lack of the material, which leaves gaps too 

 great to bridge over without some amount of speculation. 

 As it is, Professor Flower divides the principal varieties 

 (Phil. Trans., 1874,) into three : 



(i.) That in which the outer wall is feebly developed, 

 and transverse ridges become the prominent features, as in 

 the tapir. 



(ii.) That in which the outer wall is greatly developed 

 and more or less smooth, the transverse ridges being oblique, 

 as in the rhinoceros. 



(iii.) That in which the outer surface and edge of the 

 outer wall is zigzagged, or bicrescentic, as in the horse and 

 palseotherium. 



Eqims. The horse is furnished with the full mammalian 

 number of teeth, the dental formula being 



.3143 



The canines, however, are rudimentary in the female, whilst 

 in the male they are well developed (in the gelding they are 

 of the same size as in the entire horse) ; and the first pre- 

 molar, which has no predecessor, is also rudimentary, and is 

 lost early. A considerable interval exists between the 

 incisors and the premolars and molars, which latter are very 

 similar to one another, both in shape, size, and in the 

 pattern of the grinding surface. 



The incisors of the horse are large, strong teeth, set in 

 close contact with one another ; the teeth of the upper and 

 lower jaws meet with an "edge to edge bite," an arrange- 

 ment which, while it is eminently adapted for grazing, leads 

 to great wearing down of the crowns. An incisor of a horse 

 or other animal of the genus may be at once recognized by 

 that peculiarity which is known as the " mark." 



