Fig. 186. 



Fig. 187. 





Fig. 188. 



Fig. 189. 



Figs. 186-189. Four stages in the development of a tooth in a sheep embryo (from 

 the lower jaw) ; Fig. 186, Anlage of the enamel germ connected with the oral epithelium 

 by the enamel ledge ; Fig. 187, first trace of the dentinal papilla ; Fig. 188, advanced 

 stage with larger papilla and differentiating enamel pulp ; Fig. 189, budding from the 

 enamel ledge of the anlage of the enamel germ, which later goes to form the enamel of 

 a permanent tooth ; at the periphery of the papilla the odontoblasts are beginning to 

 differentiate. Figs. iS6, 187, and 188, X IIO 5 Fig. 189, X 4- rt > a > a > a < Epithelium 

 of the oral cavity ; b, b, b, l>, its basal layer ; c, t, c, the superficial cells of the enamel 

 organ ; d, d, d, d, enamel pulp ; /, />, p, dentinal papilla ; .r, s, enamel-forming elements 

 (enamel cells) ; <?, odontoblasts ; S, enamel germ of the permanent tooth ; v, part of the 

 enamel ledge of a temporary tooth ; u, surrounding connective tissue. 



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