THE HEAD AND NECK. 117 



tail, it will be necessary to give some slight account 

 of the characters and structure of these organs in 

 general, in order that the special descriptions may 

 be better understood. 



Every tooth may be divided into two principal 

 parts, a "crown," and a "root" (sometimes errone- 

 ously called " fang"). The part connecting the two, 

 often indicated by a constriction, is called the " neck." 

 The crown is the only part which is seen in the liv- 

 ing animal, the root being implanted in a socket in 

 the bone, just as the roots of a tree are in the ground. 

 The crown may be variously shaped — conical and 

 pointed, chisel- or awl-shaped, broad, flat, or rounded ; 

 or it may be complicated by the development upon its 

 surface of elevations or tubercles, called cusps, or by 

 variously disposed crests or ridges. The root may be 

 single, or divided into two or more conical, tapering 

 branches. 



In structure, the teeth are composed of several 

 distinct substances, differing from each other in 

 character and degree of hardness. The most im- 

 portant of these are : 



1. The pulp, a soft substance, abundantly supplied 

 with blood-vessels and nerves, constitutes the central 

 axis of the tooth, and affords the means by which its 

 vitality is preserved. This occupies a larger relative 

 space, and performs a more important purpose in the 



