THE ALIMENTARY CANAL 



225 



FIG. 93. UPPER JAW, WITH ROOTS 



OF THE TEETH LAID BARE. 

 a, incisors; 6, canine; c, first pre- 

 molar; d, second premolar; e, third pre- 

 molar; _/", molar. 



the crown, which projects above the gums, and a narrow neck 

 connecting the two. The root is composed of one or more 

 separate fangs ; the crown bears one or more points or cusps. 



At the cranial end of each jaw are six incisor teeth (Figs. 

 93 and 94, a). These are imbedded in the alveolar borders of 

 the premaxillaries and the man- 

 dible. The incisor teeth are 

 small, with a crown bearing a 

 sharp edge which is notched so 

 as to form three minute cusps. 

 The root of each has a single 

 fang. The lateral inciscrs are 

 the largest in each jaw, and 

 those of the upper jaw are larger 

 than those of the lower. 



Caudad of the. incisors, and 

 in the upper jaw separated from 

 them by a slight interval, are the canines (^), two in each jaw. 

 These are long, strong, pointed teeth, deeply imbedded in the 

 mandible and maxillaries, their large sockets causing a rounded 

 swelling on the external surface of the bones. Each has a 

 single fang and a single cusp. When the mouth is closed the 

 upper canines lie laterocaudad of the lower ones. 



Caudad of the canines there is in each jaw a considerable 

 interval free from teeth : this is called the diastema. Caudad 

 of the diastema are the premolar teeth, three pairs (c, d, e) in 

 the upper jaw and two pairs (c, d} in the lower jaw. These 

 teeth are compressed sideways, and those of the lower jaw fit 

 inside of those of the upper jaw. In the upper jaw (Fig. 93) 

 the first premolar (c] is small and usually has but a single cusp 

 and a single fang, though occasionally there is a small supple- 

 mentary cusp and fang. The second premolar is larger (d] ; 

 it has a large central cusp, with a single smaller cranial cusp 

 and two small caudal cusps, making four in all. This tooth 

 has two fangs. The third premolar (e) is the largest tooth in 

 the jaws ; it has three large cusps in longitudinal series and a 

 small cusp lying on the medial side of the first one in the row. 

 Its root has three fangs. The molar tooth (/) f the upper 



