13*2 
ON THE TEETH OF MAMMALIA. 
Elephant, &c., they are separated above and joined below; the use of this we 
shall see when considering the molar teeth. These pulps are enclosed in a 
capsule common to all. When crusta petrosa is present, it is supposed to be 
secreted by the inside of the capsule, but little is known respecting the manner of 
its formation. Having thus given a brief description of the manner of the growth 
of teeth, I shall now proceed to examine each kind of tooth in the orders of 
Mammalia, as it is not my purpose to run over their varieties in the other 
classes. 
Teeth are of three kinds. 
I. Incisores , Front or incisor teeth. II. Canini , Corner or Canine teeth. III. 
Molares , Back, Grinding or Molar teeth. The term tusk is applied to any tooth 
which projects beyond the lips. The substance, texture, and position of teeth 
differ considerably from those of other bones. All other bones are covered with 
a fibrous membrane called periosteum. This is entirely deficient in the exposed 
part of the teeth. The enamel, which does not extend farther than the gum, is 
so hard as to strike fire with steel; there is very little animal matter in it, 
though the bony part or ivory has a considerable quantity in its construction. 
The tusks of the Elephant, Narwhale, &c.,have no enamel, but they have a thin 
coating of a substance different from the ivory of the tooth. 
There is a circumstance which should, I think, be noticed here, and which if 
kept in mind will explain the great loss of substance in the teeth of Herbivorous 
animals. It is as follows. In the Carnivorous animals the lower jaw is con¬ 
fined by the nature of its socket to a simple motion upwards and downwards, 
and hence all these animals tear their food and swallow it in large pieces. 
Herbivorous animals, on the contrary; not only have the motion upwards and 
downwards, but also have the power of moving the jaw backwards and forwards, 
and from side to side, as the food they eat requires to be well bruised and 
triturated preparatory to its being digested. I now come to the more immediate 
subject of this paper, viz., the consideration of—I. Incisores. Front or Incisor 
teeth. 
Incisor teeth seem to exist in a higher state of development in the Rodentia 
(as the Dormouse, Squirrel, &c.), than in any of the other orders of Mammalia; 
and not only are they more highly developed, but I believe I may say that they 
are absolutely necessary to the existence of these animals, which certainly is 
not the case in any of the other orders. These teeth are found in all the Carnivora 
(as the Lion, Bear, Dog, &c.), but modified in their form to suit the habits of these 
animals, being in them sharp and angular, and better adapted for tearing than for 
cutting their food ; this is very well seen in the front teeth of the Common Cat. 
In most Mammalia the incisors of the upper jaw, if they have any, are inserted 
into the intermaxillary bone; the lower ones occupy a corresponding situation 
