COMPARATIVE ANATOMY. 
&<i. not only serve as natural weapons to 
the animal, but enable it to seize and hold 
its prey, and assist in the rude laceration 
which the food undergoes previous to de- 
glutition. The seal, the porpoise, and other 
cetacea,’ as the cachalot, have all the teeth 
of one and the same form, and that obvious- 
ly not calculated for mastication. They 
can only assist in securing the prey which 
forms the animal’s food. 
As the number and an-angement of the 
teeth was made by Linnaeus the basis of his 
classification of animals, it may be worth 
while to mention, that this anatomist gives 
the name of primores to the front, or incisor 
teeth; and of laniarii to the canine or cnspi- 
dati. The term of tusks is applied to such 
teeth as extend out of the cavity of the 
mouth. 
Certain classes of the teeth are entirely 
wanting in some orders, classes, and genera 
of quadrupeds ; and in other instances, the 
different descriptions of teeth, particularly 
the canine and molares, are separated by 
considerable intervals. There is no animal 
in which these parts are of such equal height 
and such uniform arrangement as in man. 
All the three kinds of teeth are found in 
the quadrumana, the carnivora, the pacby- 
demiata (excepting the two-hormed rhino- 
ceros and elephant), the horse, and those 
ruminating animals which have no horns. 
Cuvier states, that the teeth of an animal, 
whose bones dre found in a fossil state, re- 
semble those of man, in being arranged in a 
continued and imbroken series. 
In the simiee, carnivora, and all such as 
have canines longer than the other teetli, 
there is at least one vacancy in each jaw, for 
lodging the cuspidatus of the opposite jaw. 
There is a vacancy behind each canine in 
the bear. 
The horned ruminating animals not only 
want entirely the upper incisors, but they 
are also destitute of cuspidati, except the 
stag, which has rudiments of these teeth ; 
and the musk (moschus moschifer) where 
they are very long, and curved in the upper 
jaw. 
Between the incisors and grinders of the 
horse a very large vacancy is left, in the 
middle of which a small canine tootli, term- 
ed the tush, is found in Jhe male animal ; 
but very rarely in tlie female. 
The. elephant has grinders and two tusks 
in the upper jaw ; but the former only in 
the lower. The immense tusks belong pro- 
perly to the. male animal : as they are so 
small in the female, generally speaking, as 
not to pass the margin of the lip. (Corse 
in Phil. Trans. 1799, part 2. p. 208.) 
The sloths have grinding and canine teeth, 
without incisors. Tlie dolphin and porpoise 
have small conical teeth, all of , one size and 
shape, arranged in a continued line through- 
out the alveolar margin of both jaws. The 
cachalot (physeter macrocephalus) has these 
in the lower jaw only. The teeth of the 
seal are all of one form, viz. that of the ca- 
nine kind ; conical and pointed. 
The narwhal has no other teeth than the 
two long tusks implanted in its os inter- 
maxillare; of which one is so frequently 
wanting. 
The structure of the incisor teeth, in the 
rodentia, deserves attention on several ac- 
counts. They are covered by enamel only 
on their anterior or convex surface, and tlie 
same circumstance holds good with respect 
to tlie tusks of the hippopotamus. Hence 
as the bone wears down much faster than 
this harder covering, the end of tlie tooth 
always constitutes a sharp cutting edge, 
which renders it very deserving of the name 
of an incisor tooth. 
This partial covering of enamel refutes, 
as Blake has observed (“ Essay on the 
Structure, &c, of the Teetli,” p. 212), the 
opinion that the enamel is formed by the 
process of crystallization. 
The incisor teeth of these animals are 
used in cutting and gnawing the harder ve- 
getable substances ; for which their above- 
mentioned sharp edge renders them particu- 
larly well adapted. Hence Cuvier has ar- 
ranged these animals in a particular order 
by the name of rodentia, or the gnawers. 
As this employment subjects the teeth to 
immense friction and mechanical attrition, 
tliey wear away very rapidly, and would 
soon be consumed, if they did not possess a 
power of growth, by which this loss is re- 
compenced. 
These teeth, which are very deeply im- 
bedded in the jaw, are hollow internally, 
just like a human tooth which is not yet 
completely formed. Their cavity is filled 
with a vascular pulp, similar to that on 
which the bone of a tooth is formed ; this 
makes a constant addition of new substance 
on the interior of the tooth, which advances 
to supply the part worn down. The cover- 
ing of enamel extends over that part of the 
tooth which is contained in tlie jaw, as we 
might naturally expect : for this must be 
protinded at some future period to supply 
the loss of the anterior portion. Although 
these teeth are very deeply implanted in tlie 
