THE TEETH. 



241 



larly branched spaces are often seen in the dentin. These are the 

 interglobular spaces of Czermak. They represent areas in which 

 calcification has not taken place. Their number is variable ; when 

 relatively small and numerous, they appear, in dry preparations seen 

 under low magnification, as a granular layer the granular layer of 

 Tomes. 



The cementum is closely adherent to the dentin, and consists of 



Fig. 183. A, Longitudinal section through a human molar from the center of the 

 enamel layer, decalcified with dilute hydrochloric acid ; B, tangential, C, radiate, and 

 D, transverse section through the dentin of a human tooth, showing the fibrillar struc- 

 ture of the ground-substance (taken from v. Ebner, 91) : a and b, Two layers in which 

 the direction of the enamel prisms changes ; in c is seen a dentinal fiber with its sheath ; 

 e, groups of fibrils ; d, dentinal tubules. 



bone tissue, the parallel lamellae of which contain, as a rule, no 

 Haversian canals. There occur, however, cement lamellae, which 

 in places lose their bone-cells. A peculiarity of the cementum is 

 the presence of a large number of Sharpey's fibers, which are 

 especially abundant in those areas containing no bone-corpuscles. 

 These fibers are usually found in an uncalcified condition. 



The tooth=pulp is a tissue resembling embryonic connective 

 tissue, consisting of connective-tissue fibrils, branched connective- 

 tissue cells, and a semifluid, interfibrillar ground-substance. It is 

 characteristic of this tissue that the fibrils never join to form con- 

 nective-tissue fibers. It is probable that the fibrils are similar to 

 those of white fibrous (collagenous) connective tissue (possibly retic- 

 ular fibers), although there is a difference of opinion as concerns 

 this point, by observers who have given it special attention (see 

 v. Ebner, Rose). At the surface of the pulp is a continuous layer 

 of cells, the odontoblasts. These are columnar cells with basal 

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