Metazoa Rana. 269 



FIG. 130. VERTICAL SECTION OF A TOOTH. (Quain.) 



c, pulp cavity ; i, enamel, with radial and concentric markings ; 2, den- 

 tine, showing tubules and concentric lines of growth ; 3, cement (bone) ; 

 4, periosteum or bone-sheath ; 5, bone of jaw. 



character of the mucous membrane is considerably modified 

 in other 'portions of the alimentary canal 



