TOOTH FOLLICLE AND ITS CONNEXIONS 331 



isolated groups of epithelial cells disappear, but in most 

 adult teeth a few can be seen in the periodontal membrane 

 at the side of the tooth, and in many cases they are met 

 with in great abundance. 



Summary 



It has thus been shown that the enamel organ proper is 

 not continued downwards to form the Hertwig's sheath, 

 that the enamel organ terminates at the point of termination 

 of the enamel, and that the sheath is a prolongation of other 

 epithelial cells in the follicle which lie to its outer side. It 

 is shown that in man, as in other Mammalia, there is every 

 evidence that it moulds and determines the dentine of the 

 root, and is always present where dentine is laid down. 



As it is shown that the sheath is not the continuation of 

 the enamel organ, it may be considered that two separate 

 epithelial organs are formed from the tooth-band and the 

 cells derived from it the enamel organ, which is especially 

 differentiated to form enamel, and the epithelial sheath, 

 which is the form- determining organ of the dentine. 



The enamel which covers the exposed part of the tooth 

 is an epithelial product derived from the ectoderm ; the 

 dentine and cement are products of the mesoderm ; but the 

 whole tooth is surrounded at different stages of its growth 

 by an ectodermic structure, the sheath of Hertwig. 



It can, therefore, consistently be maintained that the for- 

 mation of the whole tooth depends upon the proliferation 

 of the ectodermic epithelial elements. The two structures 

 would have a common origin, but while one presides over 

 the formation of the enamel, the other is developed for the 

 determination and limitation of the growth of the dentine, and 

 as the enamel organ atrophies when the enamel is completed, 

 and only persists as the cornified cells of Nasmyth's membrane, 

 so the epithelial sheath becomes absorbed after the complete 

 deposition of the dentine, and only a few epithelial cells 

 remain as the epithelial debris of Malassez. 



It has been stated by several authors, especially by 

 C. S. Tomes (9), that in the Edentata an enamel organ is 

 present, although no enamel is formed, and in a paper 

 published in 1876 he showed the presence of enamel organs 



