PLATE I 



EXPLANATION OF FIGURES 



In reproduction the figures have been reduced one-half. 



1 Section through the enamel organ of the sixth back tooth of a 30 mm. 

 embryo. X 380. 



2 Section through the enamel organ of the si.xth back tooth of a 48 mm. 

 embryo. The mesodermal papilla has begun to form and the parts of the enamel 

 organ are beginning to differentiate. X 380. 



3 Section through the enamel organ of the sixth back tooth of a 78 mm. 

 embryo. The parts of the enamel organ are differentiated into inner enamel 

 epithelium, a stellate reticulum, a stratum intermedium, and an outer enamel 

 epithelium. X 380. 



4 Diagrammatic section through the enamel and enamel organ of an 82 mm. 

 embryo. The enamel is plainly differentiated into an older portion which shows 

 lighter and darker areas and a clear homogeneous layer which represents the 

 last formed enamel. Tomes processes may be seen entering this homogeneous 

 layer. The enamel organ is here reduced to a narrow compact mass representing 

 outer and inner enamel epithelium and stratum intermedium. X 850. 



5 Section through enamel organ, enamel, dentine, and odontol)lasts of a 92 

 mm. embryo. X 380. 



6 Section through a back tooth at birth (108 mm.). The enamel organ is 

 reduced to a few long narrow cells lying with their long axes parallel to the upper 

 surface of the tooth. X 380. 



684 



