1882.] 



the Enamel of the Teeth in Vertebrates. 



165 



Figure 2. Part of transverse section of lower incisor of rabbit, showing the mem- 

 brane (cuticula dentis) lying between enamel and enamel cells. 

 B. shows an en face view of a portion of c. 

 Obj. xg- immersion. 



Figure 3. A portion of vertical section of young tooth of an adult Raia clavata 

 (thornback), showing the formation of the cuticula by the ends of the 

 enamel cells. Obj. immersion. 



Figure 4. Longitudinal section of spine from a fin ray of the thornback, showing 

 tbe cuticula entire upon the under surface of the spine, with only frag- 

 ments left upon its upper surface. Obj. 2 inch. 



Figure 5. A portion of the cuticula of fig. 4, showing the outlines of the cells and 

 their nuclei. Obj. immersion. 



Figure 6. A portion of a transverse section of the lower incisor of rabbit, a short 

 distance below the gum. The enamel extends over the side of the tooth 

 no farther than u. A thick layer covered the front of the tooth which, 

 except at one point, has disappeared. Obj. immersion. 



Figure 7. A portion of a longitudinal vertical section of the upper small incisor of a 

 rabbit, e. m., 1, 2, 3, 4, 5, are cells of the enamel membrane drawn at 

 intervals, showing their gradual change as they approach the crown of 

 the tooth until, on its exposed portion, they form a homogeneous mem- 

 brane. Obj. F. Zeiss. 

 (The following seven sections were from teeth preserved in alcohol, without acid.) 



Figure 8. Vertical section of dermis and young tooth of Raia batis (skate). The 

 basement membrane upon the derm stands out remarkably clearly, and 

 could be seen running up over the young tooth quite to its apex. 

 Obj. F. Zeiss. 



Figure 9. The apex of vertical longitudinal section of tooth of a thornback, showing 

 the basement membrane upon that edge which was cut exactly vertical 

 to the surface of the tooth. No basement membrane can be distin- 

 guished upon the other edge, it being cut obliquely to the surface. Obj. 

 F. Zeiss. 



Figure 10. A portion of a vertical longitudinal section of a tooth papilla of a young 

 skate. The cellular pulp still extends quite up to the basement 

 membrane, which is more marked as the lines of the cells of the pulp 

 appear to run at right angles to it. Obj. F. Zeiss. 



Figure 11. Portion of. a vertical section of a tooth papilla of a thornback, in which 

 a thin layer of dentinal basis is seen under the basement membrane, 

 a small piece of which has been fortunately torn away with needles. 

 Obj. F. Zeiss. 



Figure 12. Portion of section of a tooth of the skate. Calcification has proceeded 

 from the surface as far as caL The cracks in the calcified portion 

 are produced in cutting. Most of the dentine is still uncalcified. 

 Nitric acid was added under the coverslip and has brought out more 

 clearly the basement membrane, which, however, never in any stage of 

 the tooth can be raised up by acid, as can the cuticula which lies over 

 it, a fragment of which adheres at <?> Obj. F. Zeiss. 



Figure 13. A portion of young tooth of a thornback, teased out in salt solution, 

 showing the dentinal basis to be formed by processes of the odonto- 

 blasts arranged closely side by side. Obj. F. Zeiss. 



Figure 14. Part of one of a series of vertical sections of tooth papilla of skate. In 

 B, cut vertically, the basement membrane b. m. is distinctly visible. In 

 A y cut more obliquely, it is not seen. Obj. F. Zeiss. 



