446 



BENIGN TUMOURS. 



The formation of these partitions places each papilla in a 

 separate cavity ; and concurrent with this process, small growths 

 take place npon the membrane of the mouth just as it dips 

 into the papillary cavity or follicle, which finally, by union 

 with other growths, form a lid which covers the papillae in a 

 closed sac or bag. 



Before the final closing of the follicle, a slight folding inwards 

 of its lining membrane takes place. 



This folding inwards of the membrane of the primitive groove 

 is for the purpose of forming a new cavity — the cavity of reserve 

 — which furnishes a delicate mucous membrane for the future 

 formation of the permanent teeth. By consulting the diagram 

 the reader will better understand this process. Fig. 1 shows the 



Fig. 106. 



papilla standing in the groove, and a slight folding inwards of 

 the membrane of the primitive groove near to the lid on the 

 right side. Fig. 2 makes this more apparent ; and in the other 

 Figs, we find the folded membrane considerably altered in form, 

 and increased in size, having a projection from its bottom part, 

 — the papilla destined for the production of the permanent tooth 

 detached from its follicle. — (From Simonds On the Age of the Ox, 

 &c., 1854.) 



From a study of this, it will be found that the cavity in 

 which the permanent tooth is developed is a mere detachment 

 from the lining of the primitive groove, by the formation of a 



