MOLARS. 161 



posit of dentine in the pulp-cavity. As the tooth becomes 

 smaller toward its root the table becomes smaller and nar- 

 rower and the dental star becomes narrower, but it also be- 

 comes longer from in front to behind, until it forms a distinct 

 square as it is exposed by its posterior face from the oblique 

 leveling-. 



As the incisors are worn away they seem to separate from 

 each other at the roots, for the narrower parts of the crowns are 

 held apart by their cartilaginous beds, which do not atrophy as 

 does the bone of the maxilla of the horse, when the narrow, 

 wedge-shaped roots are almost driven from their alveolar 

 cavities. 



When the teeth are worn down to their roots the gum 

 retracts and shows the yellow stubs, which are all that is left of 

 the incisive arch. (Fig. 167, h.) 



With the wearing away of the incisors the dental arch loses 

 its regular curve and becomes depressed in the middle. 



MOLARS. 



The ox has, like the horse, six molars in each arch, on either 

 side of each jaw. The arch is shorter, as the teeth are smaller. 

 The first molar is very small and each one increases in size to the 

 sixth ; but there is such a marked difference in the size that the 

 first three teeth occupy but the third of the arch, while the last 

 three complete the posterior two-thirds. 



In the ox the molars have the same compound arrangement 

 of enamel as in the horse, filled up by dentine and surrounded by 

 a layer of cement. The latter often exists in great quantity, 

 and is of a rich yellowish color. There seems to be a greater 

 difference in the relative density of the substances, and the 

 ridges of enamel stand out in sharper points as the softer dentine 

 becomes worn away. 



As in the horse, there are three temporary molars and six 

 permanent molars in each arch. 



According to Girard, the first temporary molar appears 



from the sixth to the twelfth day, following the eruption of the 



11 



