322 MICROSCOPIC ANATOMY OF THE TEETH 



is surrounded by an investing open-meshed network of 

 epithelium which extends from the upper or coronal part 

 of the follicle, enveloping the forming roots on their outer 

 aspect. 



It was shown by O. Hertwig (4) that in certain amphibia 

 the teeth are more or less surrounded by an epithelial sheath or 

 investment, and Von Brunn (2), carrying the investigation 

 farther, showed that in many mammalian orders such an 

 epithelial sheath exists ; in fact in all the specimens examined, 

 which included those of Rodents, Ungulates, and Carnivora. 

 He concluded, from his observations, that the epithelial 

 sheath which surrounds the roots of the forming teeth really 

 determines the deposition and limits of the dentine, and as 

 it were moulds the dentine of the roots, confining it within 

 certain limits and preventing its extension into the surround- 

 ing connective tissue. He says that where there is no 

 Hertwig's sheath there are no odontoblasts and no dentine, 

 that it is in fact the moulding or determining organ of the 

 dentine of the root. He was unable to find this sheath in 

 human teeth, and although its presence in Mammalia 

 seemed to indicate that it must be present also in man, the 

 material at his disposal did not show it. 



The preparations of human teeth made by Professor 

 Von Ebner also failed to reveal it, but both he and Von Brunn 

 concluded that it must be present, and would be seen if 

 suitable preparations could be made (3). 



It was considered by Von Brunn, in common with all those 

 who have described this sheath in Mammalia, that it was 

 produced by a downward growth of the inner and outer 

 layers of the enamel organ, the function of which, they 

 considered, was not only the formation of enamel but also 

 that of determining the limitation of the growth of the 

 dentine. 



The author's preparations of the follicle and tooth in 

 position above described would appear to show, however, that 

 on this point the previously mentioned authorities were 

 mistaken. It is seen that the enamel organ is not prolonged 

 beyond the point where the follicle is attached to the tooth 

 at its neck, but that the enamel organ terminates where the 

 enamel terminates. This is seen not only in all the sections 



