ANIMAL DENTISTRY, 



45 



paratus at that time is represented by a whitened ridge of 

 mucous membrane extending around the maxillary margin. 

 This ridge (gingival cushion) is the matrix from which the 

 teeth develop. At the earliest period it consists chiefly of 

 two layers of epithelial cells and basement membrane of 

 connective tissue. The outer layer consists of loosely ar- 

 ranged cells while the deep one is dense and lies in close 

 relation to the jaw, being only divided from the latter by the 

 thin connective tissue of the mucous membrane. 



1- 

 Z- 

 3 



4 

 5- 



»>-^y'T 





'^ 



'-^^^^^^^wtm->f 



(Cornevin et Lesbre.) 



Fig. ,72. 

 Section Through a Part of a Dental Follicle. 



1. Crusta petrosa. 



2. External enamel. 



3. 4, 5. Internal enamel. 



6. Dentine. 



7. Odontoblasts. 



8. Pulp. 



The following changes which the gingival cushion under- 

 goes constitute the process of tooth development: The first 

 step in the direction of tooth formation is observed at about 



