728 THE EXTERIOR OF THE HORSE. 



a certain extent, be compared to the lingual surface (avale) of the tooth of a 

 ruminant animal (Fig. 315). 



This more or less deep variety of fissure of the infundibulum, which causes 

 a total or partial absence of a true external dental cavity, is more common in the 

 inferior than in the superior incisors, and sometimes renders difficult the deter- 

 mination of the animal's age. The surface of friction, as soon, as it is formed, 

 besides being very irregular, does not present in a distinct manner the two 

 circles known under the names peripheral enamel and central enamel. The latter 



FIG. 316. A superior pincer and an inferior intermediate provided with two infundibula. 



is cleft behind, in a proportion which varies with the width of the fissure, and 

 its extremities become continuous on each side with the peripheral enamel. 



It is, without doubt, this type of tooth which Johann Schlechter, of Vienna, 

 has taken for a type of development of the incisors of the horse. 1 It is only a 

 question here of a malformation of the reflection of the enamel, otherwise some- 

 what rarely observed upon the whole of the arcade, but more common on the 



1 Johann Schlechter, Ueher Bau und Form der Zahne bei dem Pferde und seinen Vorfahren, 

 in (Esterreichilche Monatschrift fur Thierheilkunde, etc. (January, February, and March 

 numbers, 1831). 



