142 DIGESTION. 



Pulp-Cavity. In the interior of each tooth, extending 

 from the apex of the root or roots into the crown, is the pulp- 

 cavity, which contains a collection of minute blood-vessels and 

 nervous filaments, held together by longitudinal fibres of the 

 white fibrous tissue. This is the only portion of the tooth 

 endowed with sensibility. Its blood-vessels and nerves pene- 

 trate by a little orifice at the extremity of the root. 



The dentine and enamel of the teeth must be regarded as 

 perfected structures ; for when the second or permanent teeth 

 are lost, they are never reproduced, and when these parts are 

 invaded by w r ear or by decay, they are incapable of regen- 

 eration. The integrity of the pulp, even, is not necessary to 

 the stability of the teeth; for examples are numerous in 

 which the pulp loses its vitality from various causes, and yet 

 the tooth remains, is as serviceable as ever, being only dis- 

 colored by the decomposition of the structures in the pulp- 

 cavity, which can neither escape nor become absorbed. 



The descriptive anatomy of the teeth in the human sub- 

 ject shows how well calculated they are to perform their 

 varied functions, and how admirably they are adapted to a 

 diet composed of articles derived from both the animal and 

 vegetable kingdom. The thirty-two permanent teeth are 

 divided as follows : 



1. Eight incisors, four in each jaw, called the central and 

 lateral incisors. 



2. Four canines, or cuspidati, two in each jaw, just back 

 of the incisors. The upper canines are sometimes called the 

 eye-teeth, and the lower canines, the stomach-teeth. 



3. Eight bicuspid the small, or false molars just back 

 of the canines ; four in each jaw. 



4. Twelve molars, or multicuspid, situated just back of 

 the biscuspid ; six in each jaw. 



The incisors are wedge-shaped, flattened antero-posteri- 

 orly, and bevelled at the expense of the posterior face, giving 

 them a sharp cutting edge, which is sometimes perfectly 

 straight, but is generally more or less rounded. The upper 



