THE TEETH. 



103 



lines running parallel to the surface. These are the " brown, 

 parallel stripes of Retzius" They pursue a somewhat curved 

 course. No unity of opinion exists about their significance, 

 one (Hertz) attributing them to deposits of pigment, another 

 (Von Bibra) to the pres- 

 ence of the oxide of iron. 

 Still other striae are ob- 

 served, and are thought 

 to represent the zigzag 

 or spiral course of the 

 enamel prisms. It is 

 observed that when the 

 prisms are isolated, which 

 can be accomplished by 

 immersion in a dilute hy- 

 drochloric acid solution, 

 they have a somewhat 

 spiral form, and have 

 bulging sides and cross 

 markings, the signifi- 

 cance of which will be 

 alluded to at another 

 place. 



Near the line of the 

 dentine there are spaces 

 between the prisms which 

 are continuous with the 

 cavities in the dentine. 

 These are called the in- 

 terglobular spaces of 

 Czermak. They also oc- 

 cur at irregular intervals 

 in the dentine. 



% T n Trrmno* cnVnrtc section, magnified 15 diameters. 1, enamel with decussating 

 111 7 IDjeC . and parallel string ; 2, dentine with Schreger's lines ; 3, eel 



there is a delicate mem- 

 brane covering the sur- 

 face of the enamel. It is composed of laminated epithelial 

 scales, and corresponds to the corneous layer of the skin, of 

 which, indeed, it represents the vestiges. 



The dentine or ivory (Fig. 38, 2) consists of a dense and 

 hard matrix impregnated with the salts of lime. It contains 



FIG. 38. Premolar tooth of the cat, in situ. Vertical 



and parallel striae ; 2, dentine with Schreger's lines ; 3, ce- 

 ment ; 4, periosteum of the alveolus ; 5, inferior maxillary 

 bone. (Waldeyer.) 



