POSITION AND STRUCTURE OF HORSE 35 



front of it, that is to say, the last premolar. With 

 this exception, each cheek-tooth in an adult horse 

 is always more worn than the tooth immediately 

 behind it. 



With the exception of the first and last, which 

 are more or less pointed at the free end, an upper 

 cheek-tooth of a horse consists of a square prism 

 rather more than an inch in diameter, and about 

 three inches in height when unworn, with its lower 

 extremity terminating in four roots. Both the 

 outer and inner surfaces are marked by strong 

 vertical tlutings ; and when in use, only a small 

 extent of the upper part of the crown is exposed 

 above the gum. 



As these teeth are usually seen in a more or 

 less worn condition, it is preferable to take such a 

 partially worn tooth as the basis for a description of 

 their leading characteristics. Such a tooth may be 

 compared in structure to the incisors ; its apparent 

 complexity of structure being due to the pushing-in, 

 on the summit of the crown, of two pits compar- 

 able to the single pit, or "mark," in the incisor. 

 These two pits are the two irregularly-shaped 

 islands seen in the middle of the crown in A of the 

 illustration on page t,;^. The centres of these pits, 

 which extend right down to the base of the crown 

 of the tooth, are filled with cement ; and the walls 

 of enamel with which they are lined are thrown 

 into a number of more or less complex foldings. 



