398 DIGESTIVE SYSTEM OF THE HORSE 
alveolus, so that the masticatory surfaces of the first and second lower incisors 
are at first oval, with the long diameter transverse; 
Infundibulum later—at about fourteen years usually for the first 
i lower incisors—they are triangular, with the base 
Central enamel 
P pent "al at the labial edge. At the same time the infundib- 
er ver ) 
f ulum or “cup’’ becomes smaller, approaches the 
enamel 
lingual border, and finally disappears; it remains 
longer on the upper incisors, as it is deeper in 
them. Another marked feature in old age is the 
progressive approach to a horizontal direction as 
seen in profile; at the same time the exposed 
crowns of the teeth become parallel and finally 
convergent. 
Canine Teeth.— These are fourin number in the 
male; in the mare they are usually absent or rudi- 
mentary. They interrupt the interdental space, 
dividing it into unequal parts. The upper canine 
Cement 
Peripheral enamel Cement 
Dentine 
Central enamel 
Cement 
Fic. 338.—LoneGirupInaL Secrion oF Fig. 339.—Cross-secTION OF LOWER INcISOR TooTH oF HorRsE, 
Lower Inctsor Toorn or Horse. T, Infundibulum. 
C, Pulp cavity. Cement is shown in the 
infundibulum, but is not marked. 
is situated at the junction of the premaxilla and the maxilla; the lower canine is 
nearer the corner incisor. The canines are simple teeth, smaller than the incisors, 
Fic. 340.—Lower InctsoR AND CANINE TEETH OF Fic. 341.—Uprer INctsor anp CANINE TEETH OF 
Horse, Frve Years Op. Horsek, Five Years Op. 
The lingual border of the third upper incisor is unworn. J', I?, 73, Incisor; C, canine. 
and are curved with the concavity directed backward. The exposed crown in the 
1 Tt is interesting to notice that vestigial canines are not at all uncommon in mares, espe- 
cially in the lower jaw. They are very small, and do not usually erupt; their presence is indi- 
cated in the latter case by a prominence of the gum. This is in conformity with the fact that 
they were present in both sexes in Eocene and Miocene ancestors of existing equide. 
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