1208 



THE ORGANS OF DIGESTION 



The roots of the temporary molar teeth are smaller and more diverging than 

 those of the permanent set, but in other respects bear a strong resemblance to them. 



Permanent Teeth (denies permanentes] (Fig. 918). The incisors or cutting teeth 

 (denies incisivi) are so named from their presenting a sharp cutting edge, adapted 

 for incising the food. They are eight in number, and comprise the four front 

 teeth in each jaw. 



The crown is directed vertically and is chisel-shaped, being bevelled at the 

 expense of its lingual surface, so as to present a sharp horizontal cutting edge. 

 Before being subjected to attrition this edge presents three small elevations. The 

 labial surface is convex, smooth, and highly polished. The lingual surface is con- 

 cave, and is marked by two marginal ridges extending from an encircling ridge 

 at the neck to the angles of the cutting edge of the tooth. The ridge at the neck 

 is termed the cingulum or basal ridge. The neck of the tooth is constricted. The 

 root is long, single, conical, transversely flattened, thicker before than behind, 

 and slightly grooved on either side in the longitudinal direction. The root may 

 be curved. 



FIG. 919. Right half of upper jaw (from below), 

 with the corresponding teeth. The letters and 

 numbers point to the classes of teeth and the numbers 

 in classes. 



FIG. 920. Right half of lower jaw, with the cor- 

 responding teeth. The letter and numbers point to 

 the various cusps or their modifications on the differ- 

 ent teeth. (Burchard.) 



The incisors of the upper jaw are altogether larger and stronger than those of 

 the lower jaw, the central incisors being larger and flatter than the lateral incisors. 

 They are directed obliquely downward and forward. 



The incisors of the lower jaw are smaller and flatter than the upper, and the 

 elevations upon their lingual faces are not marked. The two central are smaller 

 than the two lateral incisors, being the smallest of all the teeth. The roots of these 

 teeth are flattened laterally. 



The Canine Teeth (denies canini) are four in number, two in the upper, two in 

 the lower jaw one being placed distal to each lateral incisor. They are larger and 

 stronger than the incisors, especially in the roots, which are deeply implanted 

 and each causes a well-marked prominence of the process at the place of inser- 

 tion. 



The crown is large, of spear-head form, and its very convex labial surface is 

 marked by three longitudinal ridges. The concave lingual surface is also marked 

 by three ridges which unite at a basal ridge. The point or cusp is longer than in 

 the other teeth, and is the point of division between a short proximal and a long 

 distal cutting edge. These two edges form an obtuse angle with each other. 



