THE TEETH. 57 



Besides these vacuities, the cement occasionally presents 

 peculiar sinuous cavities, which are certainly pathological pro- 

 ducts (see Mikr. Anat., II, 2, p. 82, fig. 202) j and frequently 

 canals, like dentinal canals (fig. 192), which are sometimes 

 closely set, at others more isolated, occasionally ramified, and 

 very frequently connected with the ends of the dentinal canals, 

 and with the canaliculi of the osseous lacunae. 



[In the cement of the Solipedia, the osseous lacuna with 

 their canaliculi, of the innermost layers, are frequently inclosed 

 within actual cells, as Gerber first pointed out. If such cement 

 be macerated in hydrochloric acid, these cells may be readily 

 isolated, and present the following characters, which are not 

 unimportant in their bearing upon the nature of the lacunas : 

 1. The lacunas 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 lacunas 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 last-mentioned 

 lacunas, in fact, it is easy to demonstrate, by the aid of acetic 

 acid, a special wall, which is at first thick, but subsequently 

 becomes thinner; and occasionally such lacunas, with walls 

 which give off a few processes externally, may be isolated. 

 These lacunas are frequently empty, but in other cases they 

 contain a substance which at first also resists hydrochloric acid, 

 wherein, however, I could discover no nucleus. 1 ] 



1 [The structure of the cement on the fang of the still uncut molar of the calf, is 

 very peculiar and instructive. It is here a white, friable substance, about ? ' th of 

 an inch thick, bounded externally by a delicate Nasmyth's membrane. Its outer 

 three fourths are composed of straight parallel fibres, resembling those of the enamel, 

 but g'gth of an inch long. The inner fourth consists of similar fibres inextricably 

 interlaced, cemented into a mass by a calcareous deposit, and containing here and 

 there, spaces or lacuna?, Tg l g 3 of an inch in length, as it were left among the fibres. 

 This structure appears to become obliterated with age, as the cement on the 

 fang of the molar immediately in front of this, which had cut the gum, had the 

 ordinary appearance. (Huxley, 1. c.) — Eds.] 



