170 A MANUAL OF DENTAL ANATOMY. 



the following extract from the paper by my father and Mr. 

 De Morgan, above alluded to : " We see the boundary of 

 the original lacunal cells only in those cases where the 

 lacunae have but few, or are entirely devoid of canaliculi. 

 It would appear to be a law, to which there are few, if any, 

 exceptions, that when anastomosis is established between 

 adjoining lacunse, the lacunal cells blend with the con- 

 tiguous parts, and are no longer recognisable as distinct 

 bodies." 



According to Kolliker, the cementum first is deposited in 

 isolated scales, which coalesce with one another, rather than 

 in a continuous sheet. In the teeth of the Primates, the 

 Carnivora, Insectivora, &c., the cementum, at least in any 

 appreciable thickness, is confined to the roots of the teeth. 

 Various reasons, however, exist, for regarding Nasmyth's 

 membrane as an exceedingly thin layer of cement, which 

 have been entered into in the section relating to that 

 structure, and need not be recapitulated here. It will 

 suffice to say, that it appears to be one of those structures 

 midway betwixt full calcification and full vitality, and 

 shares with such substances the power of resistance to 

 chemical reagents which characterises them. 



M. Magitot states that the calcification of the cartilaginous 

 cement organ of Herbivora differs in no respect from that of 

 other cartilages, but in his description he merely states that 

 patches of calcification appear here and there in the deepest 

 portion of the organ, coalesce, and come to invade its entire 

 thickness ; and further that the cement at the period of 

 eruption is constituted of " osteoplasts " regularly grouped 

 round vascular canals, and included in a ground substance 

 finely striated. (Journal del'anatomie, 1881, p. 32.) Where 

 mtra-cartilaginous ossifications occur elsewhere in the body 

 a temporary bone is formed by the calcification of the 

 cartilage matrix, which is subsequently absorbed and swept 

 away, as marrow-containing channels appear in it, and bore 



