262 COMPARATIVE ZOOLOGY OF CHORDATES 



Fig. 121. — Transverse sections through the lower jaw of mammalian 

 embryos showing the development of the teeth. 



A, early stage, the dental lamina (dl) has grown in from the ectoderm ; 

 B, a tooth-germ has been formed on the dental lamina, the cells of which 

 (ectodermal) produce the enamel (e) ; beneath the enamel the mesodermal 

 cells produce dentine (dn). C, the development of the first or milk-tooth 

 imt) is nearing completion : beneath it the dental lamina has formed 

 another tooth-germ which will produce a permanent tooth (pt) ; the 

 dentary bone (d) encloses the teeth in a socket, ftn, floor of the mouth ; /, 

 lip ; Mc y Meckel's cartilage ; mp, mesodermal papilla ; pc, pulp-cavity ; 

 t, tongue. (C/. Method of development of the denticle, Fig. 120.) 



