176 AGE OF THE DOMESTIC ANIMALS. 



INCISORS. 



The incisors are eight in number. They are set firmly in 

 tlieir alveolar cavities in tlie maxilla, and form an arch more 

 convex than either the incisive arch of the horse or the ox. As 

 in the ox, they are termed the piiicJier, first intermediate, second 

 intermediate, and corner teeth. As in the other animals, there 

 are two sets, the temporary incisors and the permanent incisors. 

 The temporary incisors are much smaller and proportionately 

 mucli narrower than the permanent ones ; so that the jaw of the 

 lamb has an elongated, narrow appearance, which alters greatly 

 in form, becoming wider and more flat in the older animals. 

 The incisors of both dentitions are wedge-shaped like the per- 

 manent incisors of the horse. They have no neck separating 

 the crown from the root, like the incisors of the ox and the 

 temporary incisors of the horse. They are firmly imbedded in 

 their alveolar cavities, which allows them to nip the short grass 

 close to the roots and obtain a living, where the ox, with its 

 loose incisors, can no longer obtain a hold to tear up the 

 blades. 



Tn the virgin tooth the extenial face is white and polished 

 except near the root, where it is surrounded by a black cement. 

 The internal face has two longitudinal gutters divided by a little 

 crest. The gutters are filled with black cement. They repre- 

 sent by their convex anterior face, in profile, the quarter of a 

 circle. From this position they meet the cushion of the upper 

 jaw by their free extremity, like the incisors of a young horse, 

 and not by the posterior surface, as in the ox ; so tliat by use 

 they rapidly Avear the anterior border and form a table to the 

 teeth like the soliped, and not like that of their closer relation, 

 the large ruminant. The incisors of the sheep are formed of 

 dentine, surrounding a pulp-cavity which becomes filled with a 

 darker-colored deposit at an early period, and are covered with a 

 layer of enamel, which disappears toward the roots, and which 

 is covered on the sides, in the longitudinal gutters, and near the 

 gums by a black cement. 



