182 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



Fig. 85. Fig. 86. 



K 



Formation of the Cementum ; m, primary cells ; j>, their 

 granular nuclei ; n, more minutely granular blastema; o, the 

 primary cell enlarged, and receiving the hardening salts ; n' > 

 calcified blastema; p',p', stellate nuclei of fully-formed ce- 

 mental cells. 



ployed wholly in forming the walls of the pris- 

 matic cells. The disappearance of the nucleus, 

 previously to the calcification of the cell, is 

 evidently the reason of the absence of any 

 permanent space or tube in its interior unoccu- 

 pied by mineral matter. The islands of Ena- 

 mel, which are found in the midst of the dentine, 

 in the compound teeth of Herbivorous animals, 

 are formed from extensions of the same ena- 

 mel-pulp, with that which gives origin to the 

 general envelope of the tooth ( 217, c). 



216. The "Cemental pulp," or matrix of 

 the Crusta Petrosa, is in fact nothing else than 

 the capsule itself; in which, at an early period, 

 nucleated cells are found, distributed in the 

 midst of a granular blastema, which is copi- 

 ously supplied by vessels. The process of 

 calcification begins in the portion nearest the 

 dentine ; And consists, as elsewhere, in the 

 absorption of calcareous matter into the cavi- 

 ties of the cells, in the more close aggregation 

 of the cells with each other, and in the changes which take place coincidently 

 in their nuclei. These, which are at first large granular spots of a rounded 

 form, send out radiating prolongations, which extend quite to the borders of 

 the cell; and as the calcareous salts which penetrate the cell, are not depo- 

 sited in the space occupied by the nuclei, the stellate cavities, or lacunae and 

 diverging canaliculi, are left, which are so analogous to those of bone, as to 

 serve to identify the two tissues. In the cementum, as in Bone and Dentine, 

 the consolidating substance appears to consist of mineral and organic matter 

 in a state of chemical union. The boundaries of the original cells usually 

 disappear in this, as in similar cases ; so that nothing remains in the fully- 

 formed cementum, to mark its cellular origin, save the stellate lacunae which 

 represent the positions of the formerly-existing nuclei. 



Formation of Enamel ; h, primary 

 cells suspended in fluid blastemag-; 

 t , the same more fully developed and 

 become angular; j, the same be- 

 coming prismatic ; k, the nucleus 

 disappearing; I, the modified pris- 

 matic cells, filled with calcareous 

 salts, forming the spicula and fibres 

 of enamel. 





