52 



DEVELOPMENT OF TEETH 



and other vertebrates as was at one time assumed. But m 

 order to explain this very important part of the subject it will 

 be necessary to give some account of the development of the 

 teeth. The type selected is the Hcd-elK)-'. which has been 

 recently and carefully described liy Dr. Leche of Stockholm, 



Fig. 37. — Two stages lu tlie development of the teetli of a Mammal (diagrammatic sec- 

 tions). ah\ Bone of alveolus ; tJenl^ dentine ; dent.s, dental sac ; en, enamel ; 

 eu.m, enamel membrane ; eiijn~, enamel membrane of permanent tooth ; en.plp, 

 enamel pulp ; fjr, dental groove ; lam, dental lamina ; lam', part of dental lamina 

 which grows downwards below the tooth germ ; n, neck connecting germs of millv 

 and permanent tooth ; pa]), dental papilla ; pap-, dental papilla of permanent tooth. 

 (After 0. Hertwig.l 



which type has furthermore the advantage of being a " central " 

 type of mammal. The first step in the formation of the teeth 

 is a continuous invagination of the epithelium covering the jaw 

 to form a deepish wall of tissue running in the thickness of the 

 jaw ; this is perfectly continuous from end to end of the lower 

 jaw. From this " common enamel germ " {Sclimelzleistc of the 

 Germans') "special enamel germs " {Sclimslzorganr, enamel organs) 

 are developed here and there as thickenings in the form of buds- 



1 Moipli. Jahrb. xix. 1892, p. 502. 



