THE DEVELOPMENT OF THE TEETH. 



137 



not remain quite that simple line of cells of which it con- 

 sisted when first formed, but varicosities, made up of poly- 

 hedral cells, bud out from it. 



The origin of the dental germs of the permanent teeth 

 remains to be described : the twenty teeth which have 

 deciduous predecessors being derived from parts of the 

 germs of these, the twelve true molars having a distinct 

 origin. About the sixteenth week of intra-uterine life, from 

 the neck of cells which connects the enamel organ of the 

 temporary enamel germ with the stratum Malpighi, there 

 buds out a secondary inflection of epithelium, similar in 

 appearance to the first rudiment of the enamel germ of 



FIG. 66 J . 





the milk tooth ; it passes down to the inner side of the 

 temporary tooth sac, and by undergoing a series of changes 

 in all respects analogous with those resulting in the forma- 

 tion of the temporary tooth germ, gives rise to the perma- 

 nent tooth germ. 



(!) Dental germ of temporary tooth of an Armadillo, showing its enamel 

 organ, and the enamel germ of the successional permanent tooth to the 

 left of it. 



