224 
MANUAL OF MODERN FARRIERY. 
but the sides of the triangles are all of one length. (See 
plate y. fig. 6.) 
At eighteen years, the lateral portions of the triangle 
lengthen in succession. First the nippers, then the dividers, 
and afterwards the corner teeth. 
At nineteen, the angles begin to wear off, the central 
teeth are again oval, but in a reverse direction, that is, 
from forward, inward, and the lower nippers are flattened 
from one side to the other. 
This triangular form is not very much developed in the 
beginning, the edges being slightly rounded, and the three 
sides are very nearly equal in length; afterwards, the 
lateral portions grow longer, whilst the anterior or outer 
side appears to diminish, the extremities become angular; 
and this lengthening in a short time is so great, that at 
from nineteen to twenty years of age the incisors have in 
reality become flattened from one side to the other. This 
flattening proceeds in succession from the nippers to the 
dividers, and from them to the comer teeth, in such a way 
as to enable us to distinguish the age of the horse up to 
twenty-two to twenty-three years. 
At twenty, the dividers are of the same shape, and at 
twenty-one, the whole teeth have acquired this form. 
After this period the incisors do not exhibit any par¬ 
ticular characters whereby to guide us in determining the 
age of a horse. They gradually become more flattened, 
converging towards each other, and touching merely by 
their lateral and anterior edge. Gradually they become 
dried, and the gums whitened, the tables of the teeth 
assume a greyish cast, the incisors in their whole extent 
are frequently incrusted at their base by a thick coating of 
tartar. The jaw-bones also become narrow. 
In consequence of the continual growing up of the teeth 
