214 
MANUAL OF MODERN FARRIERY 
to much more friction than the cutting teeth in grinding 
down the harder portions of their food and nature has 
made ample provision for their strength and endurance. 
We have given a representation of the section of a grinder 
(plate v. fig. 12) to show its interior structure. The teeth 
are prepared and formed in cavities within the jaw-bones. 
In the unborn animal a delicate membraneous bag, contain¬ 
ing a jelly-like substance, is situate in the small cell within 
the jaw-bone. By degrees this substance assumes the form 
of a tooth, and then the jelly within the membrane begins 
to change to a bony consistence ; then a hard crystallization 
is formed on the outside of this membraneous covering. 
This is the enamel of the tooth. In the formation of each 
grinder of the horse in the upper jaw, there are originally 
five of these membraneous bags filled with jelly, and four 
in the lower jaw. This jelly is gradually superseded by 
bony matter, which is deposited by little vessels penetrating 
into it. These vessels are represented by the black streaks 
in the darker central portions of the figure, around each of 
which the crystallization of enamel can be distinctly traced, 
so that there would be five distinct bones or teeth. The 
white spaces in the figure represent a very powerful cement, 
which unites all these distinct bones into one compact body, 
thus making one tooth of the five as they originally ap¬ 
peared to be ; this being accomplished, an outer coating of 
enamel invests the whole of the sides, but not the top, 
which completes the tooth. It will thus be manifest that 
this is a beautiful and perfect contrivance to prevent the 
wearing down of the grinders by the constant friction to 
which they are subjected by chewing the harder portions of 
their food. Thus it will be seen there are columns of 
enamel penetrating through the entire substance of the 
tooth ; this, together with the bony matter and cement by 
