EXPLANATION OF THE PLATES. 



DEVELOPMENT OF THE TEETH.— Plate I. page 1. 



ft. Fig. 1. A tooth-gemi — a bulging on a mucous membrane. 



b. Diagrams illustrating the three stages of dentition. 

 Fig. 1. Follicular. 2. Saccular. 3. Eruptive .stage, 



c. Diagiams illustrative of the formation of a temporary ami its 



corresjionding pennanent tooth from a mucous membrane. 

 Fig. 1. Mucous membrane. Fig. 2. Mucous membrane, •with a gra- 

 nular mass dejiosited in it. Fig. 3. A furrow or groove on 

 the granular mass. (Primitive dental groove.) 



Fig. 4. A papilla (a tooth germ) on the floor of the groove. 



Fig. 5. The papilla enclosed in a follicle in the bottom of the groove 

 (the latter in the condition of a secondarj- dental groove). 



Fig. G. The i)apilla acquiring the configuration of a pulp, and its sac 

 acquiring opercula. The depression for the cavity of re- 

 serve behind the inner operculum. 



Fig. 7. The papilla become a pulp, and the follicle a sac, in conse- 

 quence of the adhesion of the opercular lips. The second- 

 ary dental groove in the act of closing. 



Fig. 8. Tlie secondary groove adherent, except behind the inner 

 operculum, where it has left a shut ca\'ity of reserve for the 

 formation of the pulp and sac of the permanent tooth. 



Fig. 9. Tlio last change rendered more complete by the deposition of 

 the granular body (the enamel organ of Himter, Purkinje, and 

 Rixschkow). Deposition of tooth substance commencing. 



Fig. 10. The cavity of reserve receding from the surface of the giim, 

 and dilating it at its distal extremity, in which a pulp is 

 foniiing. Rudimentary opercula developing near its proximal 

 extremity and dividing it into a follicular and an extra-folli- 

 cular compartment. Temjiorary tooth pulp nearly covered 

 •with tooth substance, and granular body almost absorbed. 



Fig. 11. The cavity of reser\'e become a sac with a pulp, and further 

 removed from tlie surface of the gum. Temporarj' tooth pulp 

 covered with tooth substance, juul granidar l>ody absorln-il. 

 (See Hunter, Sat. Hist, of Human Ta(/i, p. 95.) 



Fig. 12. The teniporarj' tooth acquiring its fang bv the triple 



b 



