X EXPLANATION OF THE PLATES. 



action described in the paper, and its sac approaching the 

 surface of the gum. 



Fig. 1 3. The fang of the temporary tooth longer, and its sac touching 

 the mucous membrane of the mouth. 



Fig. 14. The temporary tooth sac again a follicle ; free portion of 

 the latter becoming shorter, and fang of the tooth receding 

 from the bottom of its socket. Permanent tooth sac re- 

 moving further from the surface of the gum. 



Fig. 15. The temporary tooth completed. Free portion of the sac be- 

 come the vascular border of the gum ; adherent portion 

 become what is commonly denominated the periosteum of 

 the fang, but which in fact is a triplex membrane viz. 

 mucous membrane, submucous tissue, and periosteum of al- 

 veolus or jaw bone. The permanent tooth sac much re- 

 moved from the gum, but connected with it by accord which 

 passes through the foramen behind the temporary alveolus. 



Fig. 16. The fang of the permanent tooth lengthening, and the crown 

 approaching the gum Fang of temporary tooth undergoing 

 absorption. 



Fig. 17. The same change more advanced. 



Fig. 18. The permanent tooth appearing through the gum. Shedding 

 of the temporary tooth. 



Fig. 19. The perfected permanent tooth. 



Fig. 20. The shed temporary tooth. 



d. Diagrams illustrative of the formation of the thrae molar teeth 

 from the non-adherent portion of the primitive dental groove. 



Fig. 1 . The non-adherent portion of the primitive dental groove. 



Fig. 2. The papilla and follicle of the first molar on the floor of 

 the non-adherent portion, which is now a portion of the 

 secondary groove. 



Fig. 3. The papilla and follicle of the first molar become a pulp and 

 sac. The lips of the secondary grove adhering, so that the 

 latter has become the posterior or great cavity of reserve. 



Fig. 4. The sac of the first molar increased in size, and advanced 

 along a curved path into the substance of the coronoid 

 process or maxillary tuberosity. The cavity of reserve 

 lengthened out or advanced along with it. 



Fig. 5. The sac of the first molar returned by the same path to its 

 former position. The cavity of reserve again shortened. 



Fig. 6. The cavity of reserve sending backwards the sac of the 

 second molar. 



Fig. 7. The sac of the second molar advanced along a curved path 

 into the coronoid process or maxillary tuberosity. The 

 cavity of reserve lengthened for the second time. 



Fig. 8. The sac of the second molar returned to the level of the 

 dental range. The cavity of reserve shortened for the 

 second time. 



