DENTAL INDICATIONS OF THE AGE OF A HORSE- 215 
which the different layers are united, and which fill the 
spaces between the columns, soon begin to wear away, while 
the enamel remains, thus occasioning the uneven surface 
presented by them, and which is the very best structure 
for them to possess in order to grind down the food. 
The grinders in the lower jaw, as we have above observed, 
having been only provided with four of those bags, are con¬ 
sequently smaller and narrower, and more regular in their 
form than the upper ones. They are placed horizontally in 
both jaws ; but in the lower one the higher side is within, 
and gradually shelving outwards, while in the upper jaw 
the higher side is without, and shelving inwards ; by which 
beautiful arrangement the triturating or grinding motion is 
most advantageously performed. Each of the grinders is 
different in structure and appearance, and can be respec¬ 
tively recognised with the situation of, and the jaws to 
which they belonged. 
When the foal is bom, it has the first and second 
grinders, which are large compared with the size of those 
by which they are afterwards replaced. In six or eight 
days after birth, the centre nippers make their appearance. 
These are large in comparison to the size of the jaw, and 
occupy its whole front, as represented in plate iv. fig. 1. 
In three weeks or a month the third grinders will have 
made their appearance, and within six weeks an additional 
incisor on each side of the two first, both above and below, 
will be visible, and soon after completed, and the jaw will 
have assumed the form exhibited in fig. 2. The two molars 
that the foal has at birth remain until the animal is two 
and a half years of age, at which time they are forced out of 
their sockets by the protrusion of the second set, or re¬ 
placers. But from this time there is no use in consulting 
the grinders for the age of the horse, as the best tests and 
