32 ELEMENTS OF HIPPOLOGY. 



taining the depression, but for another year the discoloration of 

 the body of the tooth, due to the chemical action of the contents 

 of the depression, is still more or less visible. 



As the tooth wears down and exposes the pulp cavity, its 

 secreting tissues deposit dentine to fill up the cavity, to protect 

 the nerves and blood-vessels from injury. The dentine so formed 

 is yellower in color than the original dentine of the tooth, and as 

 the tooth gets more and more worn down, assumes somewhat 

 the form of a star, hence its name, dental star. At first this 

 new dentine appears as a yellowish line in front of the enamel of 

 the mark. This is because the pulp cavity is spread out quite 

 thin near the end of the perfect tooth. It narrows and broadens 

 deeper in the tooth until its final shape is circular. The circular 

 shape is not found until the horse is about twelve, although this 

 rule is extremely elastic. 



At three or four the observer can be sure enough of the 

 horse's age without looking at the tables, but after that they 

 should be consulted. 



At five the horse's mouth presents quite positive evidence 

 of his age. Looking at the outer faces of the teeth, they appear 

 smooth and clean. The edges are sharp; there is no hook in the 

 upper corner teeth; the gums are plump; the horizontal and 

 vertical axes of the teeth are not far from equal. Looking at the 

 tables, the mark is found to be clear in all the teeth; the center 

 and intermediate teeth show tables nearly rectangular in shape, 

 and the axis of the tables at right angles to the jawbone is nearly 

 twice as long as the other one. But it is in the corner tooth that 

 the surest evidence is found. As the other incisors appear, at 

 three and four, the mark is entirely surrounded with enamel, but 

 the corner tooth comes up as a shell, with the inner wall missing, 

 and not until the tooth has been in use for from six to nine 

 months is the outer portion of the wall worn down to the level of 

 the inner portion. This peculiarity of the corner tooth at five, 

 once seen, should never be mistaken. 



