DEVELOPMENT OF THE TEETH. 

 Fig. 237. 

 c 



^s. 

 ft 



377 



Fig. 238. 



Formation of a temporary and its corresponding permanent tooth, in a sac of the mucons mem- 

 brane, a to d. Papillary stage; e to g. Follicular do. ; h to m. Saccular, do. ; n, o. Eruptive stage ; 

 p to t. Falling oat of first set. 



From the manner in which the primary tooth-sacs are formed 

 i. e. by elevations of the mucous membrane around the papillae, as 

 shown in Fig. 237, d, e it follows that the papilla, even after attain- 

 ing to the form of the body of the future tooth, 

 does not cause the layer covering it, of the ori- 

 ginal mucous membrane of the mouth, to come 

 into contact with the layer which has closed 

 over it; and therefore a space is left between 

 these two layers the cavity in which the ena- 

 mel is formed (Fig. 238, B) from cells (the ena- 

 mel pulp) contained in it. 



The general account of the development of 

 the teeth is as follows : 1. A thin layer of den- 

 tine is formed from the vessels in the pulp, and 

 which incloses the latter like a cap. This is fol- 

 lowed by other layers within each other, the pulp itself meanwhile 

 contracting. 2. The enamel is formed from the cells in the enamel- 

 cavity ; a thin layer being at first adherent to the outer layer of 

 dentine, and which is followed by others till the requisite thickness 

 is acquired, the enamel-pulp meantime gradually disappearing. 3. 

 The body of the tooth thus being developed, the formation of the 

 fang next takes place ; the pulp of the dentine now extending into 

 the alveolus, and dividing into two or three processes if the fang is 



A. The cavity containing 

 the pulp, and the dentine 

 when formed. B. Closed 

 sac in which the enamel 

 is formed. 



