1854.] OF THE ROYAL INSTITUTION. 367 
premolars ; perpetually growing teeth require the base to be kept 
simple and widely excavated for the persistent pulp. In no mam- 
miferous animal does anchylosis of the tooth with the jaw con- 
stitute a normal mode of attachment. Each tooth has its par- 
ticular socket, to which it firmly adheres by the close co-adapta- 
tion of their opposed surfaces, and by the firm adhesion of the 
alveolar periosteum to the organised cement which invests the fang 
or fangs of the tooth. 
True teeth implanted in sockets are confined, in the Mamma- 
lian class, to the maxillary, premaxillary, and mandibular, or 
lower maxillary bones, and form a single row in each. They may 
project only from the premaxillary bones, as in the Narwhal, or 
only from the lower maxillary bone, as in Ziphius; or be apparent 
.only in the lower maxillary bone, as in the Cachalot ; or be limited 
to the superior and inferior maxillaries, and not present in the 
premaxillaries, as in the true Ruminants and most Bruta. 
The teeth of the Mammalia usually consist of hard unvascular 
dentine, defended at the crown by an investment of enamel, and 
everywhere surrounded bya coat of cement. The coronal cement 
is of extreme tenuity in Man, Quadrumana, and terrestrial Car- 
nivora; it is thicker in the Herbivora, especially in the complex 
grinders of the Elephant; and is thickest in the teeth of the 
Sloths, Megatherioids, Dugong, Walrus, and Cachalot. Vertical 
folds of enamel and cement penetrate the crown of the tooth in 
the Ruminants, and in most Rodents and Pachyderms, charac- 
terising by their various forms the genera of the last two orders ; 
but these folds never converge from equidistant points of the 
circumference of the crown towards its centre. The teeth of the 
quadrupeds of the order Bruta (Edentata, Cuv.) have no true 
enamel; this is absent likewise in the molars of the Dugong and 
the Cachalot.’ The tusks of the Narwhal, Walrus, Dinotherium, 
Mastodon, and Elephant, consist of modified dentine, which, in 
the last two great proboscidian animals is properly called “ ivory,” 
and is covered by cement. 
The Dolphins and Armadillos present little variety in the shape 
of teeth in the same animal, the teeth are often very numerous ; 
and this sameness of form is characteristic of most of the mono- 
phycdonts, 
In almost all the other Mammalia, particular teeth have special 
forms for special uses: thus, the front teeth, from being commonly 
adapted to effect the first coarse division of the food, have been 
called cutters or incisors ; and the back teeth, which complete its 
comminution, grinders or molars; large conical teeth, situated 
behind the incisors, and adapted by being nearer the insertion 
of the biting muscles, to act with greater force, are called 
holders, tearers, laniaries, or more commonly canine teeth, from 
being well developed in the dog and other Carnivora, although 
they are given, likewise, to many vegetable feeders for defence 
or combat: e. g. Musk-deer.. 
