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, t 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. 



Incwor 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 





