DEVELOPMENT OF DENTINE. 



181 



Inner surface of portion of calcified dentinal pulp, 

 forming cap of dentine ; a, inter vals and walls of pri- 

 mary dentinal cells ; 6, walls of dentinal tubes ; c, nu- 

 clear matter, establishing arese of dentinal tubes. 

 For clearer demonstration, the number of tubes in 

 tlie area of each cell is made less than in nature. 



of parent cells; whilst the " se- Fig. 84. 



condary curvatures" are accounted for 

 by the fact, that the elongated nuclei 

 usually unite with each other at ob- 

 tuse angles, and not in perfectly straight 

 lines, (Fig. 83, d.) Thus we are to 

 regard the Dentine as composed of the 

 original cells of the pulp, which have 

 become consolidated by the calcifying 

 process, in every part save that which 

 is occupied by the rows of granules 

 or incipient cells, developed from the 

 metamorphosed nuclei. The calca- 

 reous matter appears to be chemically 

 united, as in Bone, with an animal 

 base ; the cavity of each cell being 

 pervaded by both ; so that, when the 

 whole of the calcareous matter is re- 

 moved by dilute acid, a cartilaginous- 

 looking mass remains, which preserves 

 the form of the tooth. The calcifying process takes place first on the exterior 

 of the pulp, and gradually extends inwards ; and the capillary blood-vessels alto- 

 gether retreat from the calcifying portion, and form their terminal loops upon 

 the surface of the part which still remains unconsolidated. As the calcifica- 

 tion extends inwards, the pulp, of course, progressively decreases ; fewer 

 nuclei are formed in the cells ; and these do not acquire so large a size. Here 

 and there it is seen, that the inner extremities of two of the granular tracts, 

 in the part last calcified, converge, and connect themselves with a single tract 

 in the layer nearer the centre of the pulp, (Fig. 83, g) ; in which we see the 

 origin of the bifurcation of the tubuli. This bifurcation becomes more fre- 

 quent, as the calcifying process approximates towards the centre and base of 

 the pulp ; and it is thus that the main tubes are formed. In some of the cells, 

 at and near the central and basal part of the pulp, the nucleus undergoes no 

 division ; but it merely elongates, and sometimes becomes angular or radiated, 

 thus showing a form of transition to the stellate nucleus of the bone-cells. 

 As already stated, we occasionally find modifications of the dentine in this 

 situation, which closely resemble true bone in structure. 



215. The Enamel-pulp is not formed -until after the dental papilla has 

 become inclosed in a capsule, by the process to be presently described ( 217, 

 c). It differs from the dentinal pulp, at its first formation, in the more fluid 

 state of its blastema ; and in containing fewer and more minute cells. The 

 enamel-pulp is derived from the free inner surface of the capsule ; of which 

 we may regard its cells as the epithelium. The cells are largest and most 

 numerous in that portion of the pulp which most nearly approaches the den- 

 tal papilla ; and many of them show a nuclear spot (Fig. 85, A, A). In the 

 portion of the enamel-pulp most distant from the capsule, the cells, at first 

 spherical, become impacted against one another, and are pressed into hexago- 

 nal or polygonal forms (i, i) ; the fluid blastema being now almost excluded from 

 between them. In the part in closest contiguity with the surface of the den- 

 tinal pulp, the cells increase in length, either by the elongation of each indi- 

 vidual cell, or by the coalescence of several (j) ; the nuclei (k) disappear - T and 

 the cells, now forming long prisms (/), absorb into themselves calcareous salts, 

 which henceforth completely fill them, in a clear and crystalline form. These 

 salts would not seem to be united^ as in bone and dentine, with any organic 

 matters; the small quantity of this existing in Enamel, being probably em- 



