THE DIGESTIVE SYSTEM 69 



The teeth have been described in connection with the 

 bones of the cranium. There are two long pairs of chisel- 

 like incisor teeth, one pair in the upper and one pair in the 

 lower jaw. The lower pair protrudes farther into the 

 mouth cavity than the upper. The upper incisors incline 

 slightly backward. The lower extend forward from the an- 

 terior end of the under jaw, curving upward to their 

 points which lie a little behind the tips of the upper in- 

 cisors when the jaw is closed. Immediately behind the 

 incisor teeth is the toothless region, the diastema. The 

 three upper and three lower molar teeth for grinding the 

 food torn loose by the incisors, are back of the disastema. 

 The mouth cavity comprises two parts, the vestibule 

 lying between the teeth on the one hand and the lips and 

 cheeks on the other, and the mouth cavity proper. The ves- 

 tibule is composed of two completely separated parts — the 

 incisor and the molar. The former lies between the incisor 

 teeth and the lips. On the lower jaw it is well developed, 

 but on the upper is almost completely lacking on account 

 of the cleft in the upper lip. The molar region of the vesti- 

 bule is a narrow region between the molar teeth and the 

 cheek. The discontinuity of the two parts of the vestibule 

 is due to the absence of teeth in the diastema. The folds 

 of the upper and lower lips and cheek are the only struc- 

 tures on the lateral side of the mouth in the diastema re- 

 gion. The mouth cavity proper is widest in the region of 

 the molar teeth. It decreases in width anteriorly and be- 

 tween the tongue and soft palate extends back as a nar- 

 rowed passage opening into the pharynx through the 

 isthmus faucium at the posterior epd of the soft palate. 



The roof of the mouth comprises two regions, the hard 

 palate supported by the palatine processes of the premax- 

 illary, maxillary, and palatine bones, and the soft palate, 

 which consists of a boneless, flexible wall extending back- 



