88 TOPOGEAPHICAL ANATOMY OF THE 



Owing to a peculiarity in the disposition of the tissues of the teeth, 

 the chewing surface of the horse's incisors presents, a characteristic 

 appearance. In the tooth that has not been subjected to wear, the 

 enamel is deeply folded into Avhat, from its funnel-like form, may 

 conveniently be called the " infundibulum." The ridge round the 

 infundibulura at this time consists of enamel, and is higher and thicker 

 in front than it is behind the depression. The infundibulum contains a 

 certain amount of cement, as do also the inequalities on the surface of 

 the crown. When the tooth has been used to a certain extent, the 

 enamel surrounding the infundibulum becomes worn through, and the 

 underlying dentine is exposed. The ridge in front of the infundibulum 

 is worn through first since it is slightly higher than that behind. In a 

 little time the infundibulum is surrounded by three rings of alternating 

 enamel and dentine. There is a ring of enamel that lines the infundi- 

 bulum, and outside this a ring of dentine, surrounded in its turn by 

 another ring of enamel. A certain amount of cement is present within 

 the inner ring and outside the outer ring of enamel. 



With the advance of age it is obvious that the infundibulum will 

 gradually wear out, and, seeing that the pulp-cavity extends into the 

 crown beyond the deepest part of the infundibulum, it is clear that the 

 sensitive pulp will become exposed unless some jarovision is made to 

 prevent this. As the tooth ages the pulp is gradually converted into a 

 variety of dentine, with the result that, when the infundibulum has been 

 worn away completely, the dentine that has replaced the pulp shows on 

 the chewing surface of the incisor as a dark-coloured island in front of 

 the place occupied formerly by the infundibulum. 



With advancing age also the embedded part of the crown gradually 

 emerges from the tooth-socket, and the outline of the chewing surface 

 changes from an oval to a triangle. In advanced age. moreover, the 

 incisors assume a more horizontal implantation into the jaw. 



In addition to their smaller size, the deciduous incisors can be 

 distinguished from those of the permanent dentition by the greater 

 smoothness and whiteness of the crown, the presence of a constricted 

 neck, and the small size and relative shortness and flatness of the root. 



Though canine teeth are frequently either absent or of small size in 

 the female, they may be quite as large in the mare as in the male. 

 The crown of a young and comparatively unworn canine is compressed 

 laterally so as to offer two surfaces separated by moderately sharp 

 borders. The labial surface is simply convex and smooth. The lingual 

 surface, on the contrary, may be described as concave, with a thick, 

 rounded ridge occupying the greater part of the surface and arranged 

 longitudinally. The neck of the tooth is not defined. The root (so- 



