482 



SPECIAL HISTOLOGY. 



cement which occur in old teeth, present immense quantities of lacunae, 

 but these are to a great extent irregular, and have mostly the elongated 



form. Many lacunae are bordered, singly 

 or in groups, by a very distinct, clear, 

 yellowish, slightly undulated margin, 

 which partially or entirely surrounds 

 them ; it has perhaps some relation to 

 the cells from which the cavities are 

 developed. 



Haversian canals do not occur in 

 young teeth, where the cement has only 

 its normal thickness ; but they are very 

 common in old teeth, especially molars, 

 and in hyperostoses one, three, or more 

 enter the cement from without, branch 

 out two or three times, and then termi- 

 nate in blind extremities. Their diameter 

 is too small (0-005-0-01 of a line), to 

 contain medulla as well as bloodvessels, and they are commonly like 

 those of the bones, surrounded by a few connective lamella?. 



Besides these vacuities, the cement occasionally presents peculiar 

 sinuous cavities, which are certainly pathological products (see " Mikr. 

 Anat." II. 2, p. 82, Fig. 202); and frequently canals, like dentinal 

 canals (Fig. 192), which are sometimes closely set, at others more iso- 

 lated, occasionally ramified, and very frequently connected with the 

 ends of the dentinal canals, and with the canaliculi of the osseous 

 lacunce. 



In the cement of the Solipedia, the osseous lacunce with their canali- 

 cuU,of the innermost layers, are frequently enclosed within actual cells, 

 as Gerber first pointed out. If such cement be macerated in hydro- 

 chloric acid, these cells maybe readily isolated, and present the following 

 characters, which are not unimportant in their bearing upon the nature 

 of the lacunae. 1. The lacunae frequently occur in twos and threes in a 

 single cell, exactly as I have seen in rickety bones. 2. The substance 

 which immediately surrounds the cavities and their processes, is not so 

 readily soluble in hydrochloric acid as the other parts of the thickened 

 cell. In fact, while the cells appear generally pale, a dark notched body, 

 which often contains a very distinct cavity, is very obvious in their 

 interior ; and as we see by comparing it with these lacunae of the cement, 

 the contours of whose cells are no longer visible, is nothing else than 

 the innermost portion of the thickened wall of the original cell. In the 



FIG. 193. Cement and dentine of the root of an old tooth : a, pulp cavity; 6, dentine ; c, 

 cement, with lacuna 1 ; c, Haversian canals. From Man. 



