216 
ON DISEASES OF THE DENTAL APPARATUS 
a circumstance never produced, as every one knows, in the normal 
state. Then the function operates according to the obliquity of 
contact, and the parallelism establishes itself by this friction be- 
tween the tables which normally would be superposed. 
This, to us at least, appears the only veritable manner to inter- 
pret this fact, of which we have had opportunities of observing 
two analogous examples upon living horses; but at these epochs 
we had not the idea of searching whether the deformity of an en- 
tire arcade was owing to the alterations of one of the molars, or to 
a disease of the bone. 
If such cases should again present themselves, it would be in- 
teresting to make this research. It would, perhaps, happen, that 
we might be able to attach to the same cause the changes which 
often enough follow — in the least degree, it is true — in the direc- 
tion of the planes of the dental tables. 
B. There is another kind of deformity of the arcades not very 
unfrequent. We have stated above, that the superior molar teeth 
were stronger and more voluminous than the inferior. This ex- 
cess of mass of the former over the latter is, perhaps, the cause 
of the exaggerated wear of the inferior teeth by the friction of 
the superior, which is so often observed. We see in this case, 
that the tables of the inferior arcades, in place of presenting them- 
selves upon the same level from the first to the last, offer a kind 
of curve, of which the concavity most profound corresponds to 
the middle teeth. This curve is formed and elevated from the be- 
ginning of these teeth to the last grinder, which experiences a less 
energetic friction on account of its position. 
In the upper jaw the plane of the table presents a disposition 
directly inverse, that is to say, it forms a salient convexity below, 
of which the most prominent part corresponds to the middle teeth. 
This kind of deformity, so frequently met with, does not place 
any obstacle to mastication ; but a period arrives when the con- 
vexity of the superior arcades, becoming more and more salient, 
imprints itself more and more deeply in the concavity of the in- 
ferior arcades; the middle teeth are then worn down to the edges 
of the alveoles, and the destruction of the gum and the bone causes 
such pain to the animal, that the trituration of fibrous aliments 
becomes impossible. 
This alteration in form of the dental arcades, and this wear of the 
edges of the alveoles, is more especially common in old horses. 
C. The inequality of the length of the dental arcades becomes 
the cause, in horses a little advanced in age, of a particular kind 
of deformity of the first superior molar and the last inferior, which 
manifests itself very often. In general, the upper range of grinders 
