XXViii INTRODUCTION, 



the modifications in the development of the dental matrix in 

 different animals and their analogies with those described by the 

 foregoing authors in the Human Subject and other mammalia are 

 detailed in the body of the present work. 



The dentinal pulp is always the first developed part of the 

 matrix, and makes its appearance in the form of a papilla, budding 

 out from the free surface of a fold or groove of the mucous mem- 

 brane of the mouth, and generally of that which covers the inner side 

 of the jaws or their rudiments. In certain fishes, as the shark, the 

 tooth is completed without the development of the matrix proceeding 

 beyond this ' papillary ' stage. 



The first papilla may be distinctly recognized in the maxillary 

 mucous groove of a human embryo, one inch in length ; the others 

 quickly follow. By the growth of the contiguous mucous membrane, 

 the papilla appears to sink into a follicle, and, by the development of 

 three or four lamellar processes from opposite sides of the mouth of 

 the follicle, and their mutual cohesion, the papilla is inclosed by a 

 capsule ; this ' capsular' stage of development is completed in the 

 human foetus at the fifteenth week(l). The capsule is the part of the 

 matrix destined for the development of the cement. In many fishes 

 and in serpents, the teeth are completed without the development of 

 the matrix proceeding beyond this stage. 



In those teeth which are defended by enamel, a pulp destined 

 for its production is developed from the inner surface of the capsule 

 opposite that to which the dentinal pulp is attached. In the human 

 subject the enamel-pulp makes its appearance as a soft gelatinous 

 substance adhering to the opercular plates closing the capsule, and 



(1) Goodsir, loc. cit. p. U. 



