374 



THE TISSUES. 



Cement and dentine of the root of an old 

 human tooth, a. Pulp cavity. &. Dentine. 

 c. Cement, with lacunae, e. Haversian canals. 

 (KtMiker.) 



Fi S- 236 - The thinnest part of the cemen- 



tum contains no lacunae, they ge- 

 nerally commencing about the mid- 

 dle of the fang, where they are 

 scattered and solitary ; and becom- 

 ing more numerous, and having 

 their lacunas freely communicating 

 towards its extremity. (Fig. 230.) 

 The thick cement occurring 

 upon old teeth, presents immense 

 numbers of lacunae, and very com- 

 monly, Haversian canals also, as 

 seen in Fig. 236. In hyperostoses 

 of the teeth, one, three, or more 

 canals are sometimes seen enter- 

 ing the cementum from without, 

 branching two or three times, and 

 then terminating in blind extremi- 

 ties. 



Cavities resembling the dentinal tubes are also sometimes found 

 in the cementum ; and which frequently communicate with the end 

 of the tubuli on the one hand, and the pores of the osseous lacunae 

 on the other. Other cavities still have been described, but they are 

 evidently pathological. 



Remarks. Thus it appears that the dentinal tubuli, and especially 

 the finest subdivisions, are homologous with the pores of bone. In 

 the latter the lacunae are added as if expansions of the pores, to 

 insure a freer circulation of the plasma from which the bone is 

 nourished; while in teeth such a development would not consist 

 with the degree of solidity and strength required in them as organs 

 of mastication. 



SECTION II. 

 THE STRUCTURE OP THE TEETH. 



The teeth consist of first, the external solid (cortical) portion ; 

 and, secondly, the internal soft portion, the pulp. The teeth are also 

 in contact with first, the gum; and, secondly, the periosteum of the 

 alveoli (the cavities in which the teeth are inserted). 



1. The cortical portion of the teeth consists of dentine, enamel, 

 and cementum, as already shown in Fig. 230. 



