CHAP. XXIII.] THE TEETH. 167 



and a root, buried in the alveolus or socket ; and the division be- 

 tween these is marked on the surface by a somewhat constricted line, 

 termed the neck. Each tooth has also an internal cavity, contain- 

 ing a vascular and nervous pulp, and which is open only towards the 

 root. Lastly, each tooth consists mainly of a peculiar modification 

 of osseous structure, termed dentine, or ivory, which is coated over 

 with calcareous enamel on the crown, and with a thin layer of true 

 bone on the root. The position and shape of the several varieties 

 of the human teeth are as follow : 



1. The incisors, or cutting teeth, are situated in front (those of 

 the upper jaw being the larger), and present a single conical root of 

 large size, and a vertical crown, bevelled behind so as to terminate 

 in a sharp horizontal edge. These teeth are fitted for cutting the 

 food. In herbivorous animals, they crop the herbage ; in rodents, 

 they are capable of gnawing even very hard substances. 



2. The canine teeth come next to, and are larger than, the incisors, 

 especially the root, which sinks deeply into the jaw, and renders the 

 alveolar arch prominent by its size. This root is conical, and the 

 crown more conical and less wedge-shaped than that of the incisors, 

 being usually surmounted with a small pointed tubercle or cusp, 

 whence they are termed cuspidate. In consequence of the small 

 size of the lower incisors, the lower canines are nearer together 

 than the upper, and fall within them when the mouth is closed. 

 These teeth in the canine, feline, and other carnivorous tribes, are 

 largely developed, and more decidedly formed for lacerating and 

 tearing the flesh of prey. 



3. The bicuspids, or false molars, are not so large as the canine, 

 which they succeed, but their crown presents two pyramidal emi- 

 nences, as their name implies, and there is a tendency in their root 

 to be double ; this part being marked by a vertical groove, and its 

 apex, sometimes bifid, being perforated by two apertures leading to 

 the interior. 



4. The true molars, or multicuspidate teeth, are placed most pos- 

 teriorly, and are distinguished by their great size, the square form 

 of their crown, surmounted by three, four, or five cusps, a distinct 

 neck, and by their shorter, but more divided root, which presents 

 from two to five branches, the inner the more divergent, and each 

 perforated at its apex. The hindermost of these are the wisdom 

 teeth. The false, and especially the true, molars are admirably 

 adapted for grinding and pounding the food, under the influence of 

 those powerful muscles by which the lower jaw is moved in a lateral 

 direction while being forced against the upper. Though the least 



