298 
On the Teeth of the Ox, Sheep, and Pig, 
in Avhich it derives its nutrition, I venture to detain the reader by 
some further remarks on the crusta. It need hardly be stated 
that according to the due supply of nutritive materials to the 
teeth, will their integrity be preserved, and their fitness for their 
important office. 
If teeth die in their sockets, they must greatly impair the 
health of the animal, from his incapability of properly masticating 
the food, as also from the suffering he will endure. The diseases 
of the teeth of animals and the causes leading- to them have cer- 
tainly not as yet received all the attention which the importance 
of the subject merits. 
To return to the Crusta. On the fangs of teeth recently 
cut, but little of this substance is met with, when compared 
with that existing on old teeth. As age advances, however, the 
Crusta increases. Hereafter it will be shown how this and the 
other structures are originally produced. It may, nevertheless, 
be now asked how the increased quantity upon an old tooth is 
accounted for ? Is the crusta always added to from the original 
source of its production, or can it be otherwise augmented? I 
answer that it frequently receives an addition altogether inde- 
pendent of its original source. As this is a novel view of the 
subject, in order to show its correctness, I must direct the reader's 
attention to two illustrations, figs, 10 and 11, taken from speci- 
mens in my possession. 
I may preface the explanation of this matter by stating that 
anatomists are generally agreed that after a given time the pulp 
ceases to produce any more dentine, and becomes converted by 
ossification into a substance which Professor Owen has designated 
osteo-dentine. This substance therefore would now fill the pulp 
cavity of the tooth. Now, however true this statement may be 
of man or of many species of animals, it does not appear to be 
positively correct when applied to, our domesticated Herbivora. 
In the horse, as an example, obliteration of the cavity is gra- 
dually effected by the pidp continuing to form dentine. This, as its 
normal action, goes on and is not supplanted by an mJnormal or 
diseased one, as it would be were the pulp to become ossified. As 
the producing organ of the dentine, the pulp simply gives way to 
its own product, which ultimately is thus made to occupy its 
place in the cavity. In proportion as the pulp diminishes so is the 
supply of nutriment to the tooth lessened, and at length entirely 
cut off from the interior. To provide for the vitality of 
the tooth under these circumstances, the Crusta increases in 
quantity on the fang at the expense of the peifecthj formed 
dentine which is lying in immediate contact with its inner surface. 
Through the medium of the canals in the Crusta, which open 
on its borders, the tooth now draws its nourishment from the 
