128 



ANIMAL BIOLOGY. 



[Part I. 



chamber is completely separated by this palatal septum from the 

 lower or mouth cavity ; but posteriorly the two chambers unite 

 where the palate ceases. Finally, the upper or respiratory 

 chamber becomes more or less completely divided into two 

 chambers by a median vertical partition (e.. Fig. 40, B.) or inter- 

 nasal septum. 



All the salivary and buccal glands of the rabbit are stomodseal 

 in their origin, and are therefore lined with epiblast and not 

 with hypoblast as in the pancreas. 



The teeth are also stomodseal structures. The manner of 

 their formation is briefly as follows : Along the line of the jaw 

 the epithelium becomes thickened. This thickened epithelial 

 keel, projecting downwards into the tissue of the jaw, is 

 known as the primary enamel germ. At the special points 

 where teeth are to be developed, the down-growth becomes 

 more marked and special enamel organs (en. or., Fig. 41) are 

 differentiated, one for each tooth. Into each enamel germ 



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FIG. 41. DIAGRAMS OF TOOTH DEVELOPMENT. 



I. Transverse section through dental ridge soon after formation of enamel 

 germ. II. Transverse section of the same at a later stage. III. Transverse 

 section through the jaw of a kitten, in which the permanent tooth is yet 

 further developed. 



d. Dentine, d. c. Dental capsule, d. p. Dental papilla, e. g. p. Enamel 

 germ of corresponding permanent tooth, en. Enamel, en. c. Enamel cells. 

 en. or. Enamel organ, ep. Epithelium of gum. od. Odontoblasts. 



there projects upwards a vascular dental papilla (d. p.\ and 

 round the enamel germ and its dental papilla the tissues become 



