DISTINCTIVE CHARACTERISTICS. 41 



tooth-lone (dentine), which constitutes the principal 

 portion of the tooth, and of the somewhat softer 

 cement (cementum), which serves in various ways 

 as material for covering and filling. A general 

 account will suffice for our purpose. The mem- 

 branous covering of the mouth-cavity like that 

 of the outer skin consists of two layers, the epi- 

 thelium (the upper skin), formed of several layers 

 of cells, and the membrane of the cutis (leather 

 skin), consisting partly of cells and partly of fibres. 

 The first sign of a tooth is a knotty protuberance 

 of the cells of the epithelium rising into the cutis. 

 Again, into this protuberance upwards there rises 

 from the cutis a cone-shaped elevation, upon which 

 there then appears the first formation in the shape 

 of a cap ; this is the enamel-germ or the enamel- 

 membrane which produces the enamel. The other 

 portion belonging to the cutis i.e. the membranous 

 tissue of cells which rises up into the epithelium 

 and is termed the dentine-germ becomes calcinated 

 into tooth-bone. But, in addition, the mem- 

 branous tissue of cells directly connected with the 

 dentine-germ produces in various measures and 

 extent the fewer- celled and softer cement round 

 about all the immediate surroundings of the tooth. 1 

 1 Baume, Odontologische Forschungen, I. Th. ; published also 



