PULPS AND SACS OF THE HUMAN TEETH. 31 



molars. It is about the fourteenth or fifteenth week that we 

 begin to observe preparations made for this provision, -by the 

 gradual appearance of a little depression in the form of a 

 crescent, immediately behind the inner operculum of each of the 

 milk-tooth follicles. The concave edges of these depressions 

 are in contact with the attached margins of these opercula. 

 Those of the centre incisives appear first, then the laterals, 

 canines, anterior bicuspids, posterior bicuspids. About this 

 time the opercula close the mouths of the follicles, but with- 

 out adhering, the anterior closing first, then the laterals, and 

 so on in succession. The lips and walls of the secondary 

 groove now begin to cohere in a direction from behind for- 

 wards, the opercula and every part of the groove, with the 

 exception of the ten depressions for the permanent teeth, be* 

 coining rough, flocculent, and adherent. The follicles have 

 now become the sacs ; the papillae the pulps of the milk-teeth ; 

 and the crescent-formed depressions vacant cavities of reserve, 

 to furnish delicate mucous membrane for the future forma- 

 tion of the pulps and sacs of the ten anterior permanent teeth. 



The general adhesion does not invade that portion of the 

 primitive dental groove which is situated behind the posterior 

 milk-molar follicle. This small portion retains its original 

 appearance, greyish-yellow colour, and smooth edges, for a 

 fortnight or three weeks longer, and affords a nidus for the 

 development of the papilla and follicle of the anterior per- 

 manent molar-tooth, the fundus of its follicle being situated 

 immediately behind the sac of the posterior milk-molar. The 

 cavities of reserve for the ten anterior permanent teeth are at this 

 period minute compressed sacs, with their sides in contact, and 

 situated between the surface of the gum and the milk-sacs. 



The papillae of the milk-teeth, from the time that their 

 follicles close,* become gradually moulded into their peculiarly 



* Herissant in the Mem. de I'Acadcmie Royale, 1754, p. 664, described 

 two grnns the " gencive permanent, " and the " gencive passagere. " His ideas 



