ALIMENTARY CANAL AND ITS APPENDAGES 399 



canines, bicuspids, and molars, arranged in a definite order in each 

 jaw. Beginning at the middle line we meet in each half of each 

 jaw with, successively, two incisors, one canine, and two molars 

 in the milk set; making twenty altogether in the two jaws. The 

 teeth of the permanent set are thirty-two in number, eight in each 

 half of each jaw, viz. beginning at the middle line two incisors, 

 one canine, two bicuspids, and three molars. The bicuspids, or 

 premolars, of the permanent set replace the milk-molars, while the 

 permanent molars are new teeth added on as the jaw grows, and 

 not substituting any of the milk-teeth. The hindmost permanent 

 molars are often called the wisdom-teeth. 



Characters of Individual Teeth. The incisors (Fig, 123) are 

 adapted for cutting the food. Their crowns are chisel-shaped and 

 have sharp horizontal cutting edges, which become worn away by 

 use so that they are beveled off behind in the upper row, and in the 

 opposite direction in the lower. Each has a single long fang. The 

 canines (Fig. 124) are somewhat larger than the incisors. Their 

 crowns are thick and somewhat conical, having a central point or 



FIG. 123 FIG. 124 FIG. 125 FIG. 126 



FIG. 123. An incisor tooth. 

 FIG. 124. A canine or eye-tooth. 



FIG. 125. A bicuspid tooth seen from its outer side; the inner cusp is, accord- 

 ingly, not visible. 



FIG. 126. A molar tooth. 



cusp on the cutting edge. In dogs, cats, and other carnivora the 

 canines are very large and adapted for seizing and holding prey. 

 The bicuspids or premolars (Fig. 125) are rather shorter than the 

 canines and their crowns are somewhat cuboidal. Each has two 

 cusps, an outer towards the cheek, and an inner on the side turned 

 towards the interior of the mouth. The fang is compressed later- 

 ally, and has usually a groove partially subdividing it into two. 

 At its tip the separation is often complete. The molar teeth or 

 grinders (Fig. 126) have large crowns with broad surfaces, on which 



