140 A MANUAL OF DENTAL ANATOMY. 



but did not present any structures essentially different from 

 those found around it. It very speedily assumes the form 

 of the apex of the future tooth, becoming, if it be a canine, 

 simply conical, if a tooth with two cusps, bicuspid; and 

 coincidently with these changes the layer of cells forming 

 its surface, which is in close relation with the enamel cells, 

 becomes differentiated from the parts beneath it. 



These cells, which become dentine by their calcification, 

 form a very distinct layer, which, after the commencement 

 of calcification, adheres more strongly to the formed cap of 

 dentine than to the rest of the pulp, and so is often pulled 

 away with the former when the two are separated ; hence 

 this layer of cells has obtained the name of " membrana 

 eboris," or membrane of the ivory ; but the student must 

 beware of falling into the mistake of supposing that it really 

 is a " membrane " properly so called. 



The individual cells, which collectively constitute the 

 membrana eboris, are called odontoblasts ; they are variable 

 in shape, differing even in the same animal according as 

 the formation of dentine is going on actively or not, but 

 are always much longer than they are broad, and are fur- 

 nished with oval nuclei near to their deeper ends. The 

 odontoblast cells are furnished with several processes, named 

 according to their direction ; thus the process which pene- 

 trates the formed dentine is called the " dentinal process," 

 that which, at its opposite pole, passes into the deeper 

 part of the pulp where it communicates with other cells, 

 the "pulp process," and those which communicate with 

 neighbouring odontoblasts, "lateral processes." Before 

 entering upon a detailed description of the transformation 

 which the various cells undergo in their conversion into 

 enamel, dentine, or cementum, it will not be out of place 

 to say a few words relative to the process of calcification 

 generally. 



But before doing so it may perhaps assist the student, who may 



