292 MICROSCOPIC ANATOMY OF THE TEETH 



enter the substance of the cement from the periodontal 

 membrane and penetrate it in more or less parallel lines. 

 These fibres are prolongations of the connective-tissue 

 bundles, and serve to attach the membrane to the tooth. 

 It is undecided if they are calcined or not. In caries of 

 cement the micro-organisms penetrate along the lines 

 of these fibres exactly as they do along the canals of the 

 dentine, which would lead us to suppose that they are not 



FIG. 186. Similar preparation to fig. 185. ( x 350.) 



so fully impregnated with lime salts as the surrounding 

 matrix. 



Haversian canals are said to be occasionally seen in the 

 cement of human teeth, but are of rare occurrence, and when 

 present are generally found in the thick portion between the 

 roots of the molars. The lamellae are arranged concentrically 

 to the canal, as in bone. Vascular canals are also occasionally 

 seen, which do not exhibit the structure of Haversian canals, 

 but simply appear as channels or perforations in the sub- 

 stance of the tissue. 



In the specimen figured (fig. 192) there were numerous 

 canals in the dentine of the root, and each of these is seen 

 to be surrounded by a layer of cement containing lacunae. 



