THE DEVELOPMENT OF THE TEETH. 159 



The dentinal process passes into the tubes of the dentine, 

 and it frequently happens that when the membrana eboris 

 is only slightly separated from the dentine these processes, 



FIG. 74 1 . 



which constitute the dentinal fibrils, may be seen stretching 

 across the interval in great numbers. 



The odontoblasts, as may be seen from figures 30 and 31, 

 are fitted closely together, and there is no room for any other 

 tissue between them, so long as the formation of dentine is 

 actively going on. Prior to its commencement, however, 

 the cells are not so square at their ends, and the appear- 

 ance of the thin edge of such a pulp suggests the idea that 

 they are bedded in a transparent and structureless jelly, 

 which projects a little beyond them. To render my mean- 

 ing more clear by a homely illustration, the surface of the 

 pulp at this stage reminds one of the clear jellies put upon 

 the table with strawberries or the like buried in them, near 

 to, but beneath, the surface. But no such substance can 

 be seen when once calcification has actively set in. 



When the pulp has completed, for the time being at all 

 events, the formation of the dentine, the odontoblast cells 

 become more elongated and more rounded in their outline 

 and taper off towards and into the dentinal process, instead 

 of having truncated ends. 



The cells figured by Lent as the formative cells of dentine 

 I regard as odontoblasts taken from an adult tooth, the 



0) Isolated odontoblast cell. 



