THE HEAD AND NECK. 137 



tinue to grow, but gradually rises towards the sur- 

 face of the socket, the bottom of which fills up with 

 bone, so that in very old horses the crowns are en- 

 tirely w r orn away, and nothing but the roots of the 

 teeth remain, loosely implanted in the jaw. If from 

 any accidental cause one of the teeth is absent, the 

 tooth opposite to it in the other jaw, having nothing 

 to wear against, will gradually rise high above the 

 level of its fellows. 



Temporary or Milk-Teeth. The first, temporary, 

 deciduous, or milk set of teeth of the horse, though 

 on the whole resembling the permanent set, having 

 the characteristic enamel foldings arranged on the 

 same general principle, present several interesting 

 peculiarities. 



The incisors are in number the same as the per- 

 manent teeth of this class. They are, however, not 

 only smaller, but, as they are only required to be in 

 use for a limited time, they have not need of the 

 lengthened crowns passing indefinitely into the root 

 possessed by the latter, and therefore show distinctly 

 the broad crown, contracted neck, and definite root 

 of the brachydont type of tooth. In this respect 

 they resemble the ancestral form from which the 

 permanent teeth have been derived. The infundibu- 

 lum or pit is present, but of comparatively little 

 depth. 



