266 COMPARATIVE ZOOLOGY OF CHORDATES 



Fig. 124. — Types of teeth (the different teeth are not drawn to the same 



scale). 



A, longitudinal section through a human molar, showing : c, cement 

 (here restricted to the base of the tooth) ; d, dentine ; e, enamel ; pc, pulp- 

 cavity ; r, roots or fangs ; such a tooth is short and low in the crown, and 

 conforms to the type called brachyodont. B, longitudinal section through a 

 premolar of the horse ; cement, dentine and enamel all enter into the com- 

 position of the crown of the tooth, and as the hardness of these substances 

 differs, they are worn away to different extents ; such a tooth is long and 

 high in the crown, and conforms to the type called hypsodont. C, longi- 

 tudinal section through the incisor of a rabbit, showing the open (" root- 

 less ") pulp-cavity or persistent pulp (pp). D, view of the crown of an 

 upper molar of a pig, showing the separate cusps characteristic of bunodont 

 teeth. E, crown of an unworn, F, crown of a worn lower molar of a 

 camel, showing the crescent-shaped ridges joining the cusps, characteristic 



