42 CAETILAGE. BONE. TEETH. 



illary bones begin to show distinct longitudinal 

 depressions or grooves, at the bottom of which minute 

 granulations make their appearance, which are the 

 germs of the teeth ; it is from these that the ivory is 

 developed. Shortly afterwards partitions make their 

 appearance by which the groove is divided up into 

 separate apartments, with a germ at the bottom of 

 each recalling in their appearance the circumvallate 

 papillae of the tongue. Still later the margins of 

 these compartments, as they grow, rise above the 

 level of the germs, contract by approaching from 

 opposite sides, and finally unite together. Hereafter 

 the germ is enveloped on all sides in a cavity which 

 takes the name of the dental sac. 



Dental sac. The walls of the sac are at first formed by two dis- 

 tinct layers, which afterwards become one. The 

 external layer, which later becomes the periosteum 

 of the socket, is made up of very vascular connecting 

 tissue ; the internal layer, of the same nature as the 

 preceding, but more delicate in structure, contri- 

 butes, according to M. Magitot,* to the subsequent 

 formation of the enamel. 



We know already that the dental germ takes its 

 origin, by a pedunculated root, from the bottom of 

 the sac ; from a point diametrically opposite to 

 this springs another germ similar to it in nature, 

 which, as we shall see hereafter, gives origin to the 

 enamel. 

 of The dental germ (whence the ivory is developed) 



* Emile Magitot has a paper on the structure of the teeth in the 

 Archives Medicates, Paris, Jan. 1858, and has sinoe>ritten on the subject 

 in same Journal. (Ed.} 



