272 DEVELOPMENT OF TEETH IN THE HORSE. 



fit the end of the jaw ; the crown is broad, and the contour 

 of the biting surface, before it is much worn, approaches 

 an ellipse. The incisors of the horse are distinguished 

 from those of ruminants by their greater length and cur- 

 vature, and from those of all other animals by the fold of 

 enamel (Fig. 55), a, which penetrates the crown from its 

 flat summit, like the inverted finger of a glove. When 

 the tooth begins to be worn, the fold becomes an island 

 of enamel, inclosing a cavity partly filled by cement, and 

 partly by the substances of the food, and is called the 

 "mark." In aged horses, the incisors are worn down 

 below the extent of the fold, and the " mark" disappears. 

 This cavity is usually obliterated in the first or mid in- 

 cisors at the sixth year, in the second incisors at the 

 seventh year, and in the third or outer incisors at the 

 eighth year, in the lower jaw. The mark remains some- 

 what longer in the incisors of the upper jaw. 



The following is the average course of development 

 and succession of the teeth in the horse {Equus cahallus) : 

 The summits of the first functional deciduous molar, c?, 2, 

 "first grinder" of veterinary authors, are usually appa- 

 rent at birth; the succeeding grinder, d 8, sometimes 

 arises a day or two later, sometimes together with the 

 first. Their appearance is speedily followed by that of 

 the first deciduous incisor — "centre nipper" of veterina- 

 rians — which usually cuts the gum between the third and 

 sixth days. The second deciduous incisor appears be- 

 tween the twentieth and fortieth days, and about this 

 time the rudimental grinder, jo 1, comes into place, and 

 the last deciduous molar, c^ 4, begins to cut the gum; 

 about the sixth month the inferior lateral, or third inci- 

 sors, with the deciduous canine, make their appearance. 

 The minute canine is shed about the time that the con- 



