is completely filled, the tooth ceases to grow, and is not pushed be- 

 yond the alveolus during wear, as is the case with the teeth of the 

 horse. 



The incisor tooth has scarcely arrived at its perfect development 

 before it begins to be worn. Its horizontal position, and its coming 

 in contact with the pad on the upper jaw, exposes the anterior border 

 and superior face to friction and consequent wear from before to be- 

 hind. The wear, therefore, chiefly affects its upper face, which really 

 forms the table of the tooth, and which is designated the Avale. 

 When use has worn away the conical eminence and the grooves bor- 

 dering it, the tooth is levelled. As wear goes on, there appears at 

 first, and at the extremities of the tooth, a yellow band, which is the 

 dentine denuded of its enamel ; and later, in the dentine, a yellower 

 transverse band shows itself. With increase of wear, this contracts, 

 then widens, and finishes by forming a mark nearly square, and then 

 round, which is the recently formed dentine that fills the pulp cavity 

 of the tooth. It is a veritable dental star, analogous to that in the 

 horse's teeth, and varying in form according to the incisor in which 

 it appears. 



In proportion as the teeth are used, they seem to separate from 

 one another, although they still remain in the same place. This is 

 because these teeth, in use, only touch each other by their extremi- 

 ties, and as they become worn they decrease in width, and are neces- 

 sarily separated to an extent varying with their degree of wear. 

 Finally, when the tooth has reached its last stage of wear, there only 

 remains the root, the upper portion of which, becoming apparent by 

 the retreat of the gum, stands as a yellow stump, very distant from 

 those which form with it the remains of the incisive arch. 



The first incisors (milk teeth) of the ox, like those of the horse, 

 are all deciduous or temporary, and differ from those which replace 

 them by their smaller volume, less width, the transparency of 

 their enamel, and their being more curved outwards. Their roots are 

 much shorter, and are destroyed by the succeeding teeth. The two 

 temporary centrals are always separated by a marked interval, de- 

 pending on the thickness of the fibre-cartilage in the maxillary sym- 

 physis during youth. 



Molars. As in solipeds, the molars are six in number in each! 

 side of each jaw, but are much smaller and form a much shorter 

 arch. Their reciprocal volume is far from being uniform, as in the 

 horse, but goes on augmenting from the first to the sixth, and to such 

 a degree that the space occupied by the three anterior molars is only 

 about one-half of that required for the three posterior ones. The last 

 molar alone occupies nearly four times as much space, lengthwise, as 

 the first. 



Their wearing surface, constructed on the same system as that 

 of the horse's molar, presents eminences a little more acute. The ar- 

 rangement of their three constituents is in principle as in the latter 

 animal. As in the horse, the three front molars are deciduous or tem- 

 porary. The period of dentition is as follows : 



