272 



STUDIES IN ADVANCED PHYSIOLOGY. 



sockets in which the teeth are held. It not infrequently 

 happens that teeth quite loose are in a short time again 

 firmly set in their places. 



Origin of the Enamel. The manner in which the teeth 

 arise originally may be tolerably easily understood by ex- 

 amining a section from the jaw-bone of a foetus, in which 

 the rudiment of the teeth are just making their appearance. 

 In such an examination it will be found that the first indi- 

 cation of teeth is a pitting in of the epithelium of the 

 mouth (the skin) in the form of a groove, which occupies 

 about that position on the jaw where later the row of teeth 

 is to appear. This groove of epithelial cells grows down 

 into the substance of the jaw, and from this groove there 

 grow out little side projections which soon begin to shape 

 themselves into the forms of the crowns of the intended 

 teeth. This epithelial outgrowth produces the enamel of 

 the teeth, so that this part of it appears in a developing 



^ 



Xg. 



(After 



Fig. 104. SECTION THROUGH A DEVELOPING MILK MOLAR OF A HUMAN EMBRYO. 



Rose.) 



L. E. L., labiodental lamina; M.E., the epithelium of the mouth; Z.L., dental 

 lamina, spreading: out at P.p. to form the enamel cap of the future bicuspidate tooth ; 

 Z. S., the condensed tissue forming the dental sac. 



tooth some time before the body of the tooth, the dentine, 

 arises. The cells of the lowest row of these lateral out- 

 growths become columnar and elongated and form the enamel 

 prisms. According to some anatomists these hexagonal 



