262 MICROSCOPIC ANATOMY OF THE TEETH 



it becomes impossible to say at what point the dentine ends 

 and the bone commences ; and this difficulty is intensified 

 by the fact that the bone of many fishes lacks lacunae and 

 is almost exactly like dentine.' l 



The Development and Calcification of Dentine. As pre- 

 viously stated, dentine is developed from the mesodermic 

 dentine papilla, which is a condensation of the cells of the 

 mesoderm beneath the previously-formed ectodermic enamel- 

 forming cells. As shown by Von Brunn (4), in several orders 



FIG. 164. Osteodentine tooth of Lamna cornubica (Porbeagle Shark). 

 Osteodentine ; central tubes radiating from medullary channels, e. Enamel. 

 Fuchsin stain by capillary attraction. ( x 50.) 



of the Mammalia the appearance of epithelial cells always 

 precedes and appears to determine the formation and limits 

 of growth of the dentine. Von Brunn and Von Ebner (6) 

 were unable to substantiate the existence of this determining 

 epithelial organ in the formation of the dentine of the root 

 in man, but as explained in the chapter on ' The Tooth 

 Follicle and its Connexions ', the author has found a similar 

 condition in human teeth. He has shown that this epithelial 

 sheath proceeds from cells of the follicle which are not 

 differentiated to form an enamel organ. This, however, 

 1 Tomes's Dental Anatomy, 7th ed., p. 100. 



