THE TEETH. 



473 





f 



parallel to the pulp cavity, and arise from the primary curvatures of the 

 uentinal canals, and which are the ex- 

 pression of the laminar mode of de- 

 posit of the dentine. In animals they 

 are at times singularly beautiful, espe- 

 cially in the Cetacea and Pachyder- 

 mata (Zeuglodon, Dugong, Elephant), 

 and also in the Walrus. Here, as well 

 as in fossil teeth, we very frequently 

 observe a breaking up of the dentine 

 into lamellae (Owen), indications of 

 which may be found also in fresh human 

 teeth and in the dental cartilage. 



Upon the crown, the dentinal canals 

 not unfrequently pass for some distance 

 into the enamel, and expand here and 

 there, into larger cavities (Fig. 191), 

 which should perhaps rather be regarded 

 as pathological. Similar not quite nor- 

 mal formations are the interglobular 

 spaces in the dentine itself (Fig. 188). 

 Czerm&k has conferred this name upon 

 certain very irregular cavities, bounded 

 by globular processes of the dentine, 



which are, it may be said, never entirely absent in the teeth. In the crown 

 they are found most frequently in the neighborhood of the enamel, and 



Fig. 188. 



often form a thin curved layer, extending along its whole inner surface, 



FIG. 187. Perpendicular section of the apex of an incisor tooth (human), magnified 7 

 diameters : a, pulp cavity; 6, dentine; c, arched contour lines, with interglobular spaces; rf, 

 cement; e, enamel, the various directions of the fibres being indicated; ff, lines of color of 

 the enamel. 



FIG. 188. A morsel of dentine with dentinal globules and interglobular spaces filled 

 with air between them ; magnified 350 diameters. 



