

DESCRIPTION OF THE PLATES. 



PLATE I. 



Diagrams of the development of the dental 

 tissues. Fig. 1. — Dentine: a, end of a 

 linear series of primary dentinal cells ; 

 «•, nucleus ; b, division of the nucleus ; 



c, c, subdivision and elongation of the nu- 

 cleolar matter, establishing secondary cells ; 



d, elongated nuclei of secondary cells 

 uniting end to end to form the areas of 

 the dentinal tubes ; e, e, calcified cap of 

 dentine formed by intus-susception of the 

 clear hardening salts into the walls and 

 cavities of the cells, and intercellular 

 blastema, e' ; and by their partial ex- 

 clusion from the moniliform nucleolar 

 tracts, f g, union of two peripheral 

 nucleolar or secondary cells with one 

 nearer the centre of the pulp. Fig. 2. 

 — Inner surface of a portion of the cal- 

 cified dentinal pulp, forming the cap 

 of dentine, which has been displaced : 

 a, intervals and walls of primary denti- 

 nal cells (' areoles' of the French Acade- 

 micians) ; b, indication of walls of secon- 

 dary cells forming the parietes of dentinal 

 tubes ; c, nucleolar matter which esta- 

 blishes the areae of the dentinal tubes, 

 (' granulations des areoles signalee, par M. 

 R. Owen,' of the French Academicians). 

 For clearer demonstration, the number 

 of tubes in the area? of the cell is made 

 less than in nature. Fig. 3. — Thin cal- 

 cified portion a, resting on b, uncalcified 

 portion of the pulp ; magnified on half 



the scale of the preceding scheme. Fig. 4. 

 — Enamel: h, primary cells suspended 

 in fluid blastema g ; i, the same angularly 

 aggregated to form the actinenchymatous 

 tissue ; j, the same, becoming cylindrical 

 by either elongation or terminal confluence , 

 k, the nucleus disappearing ; I, the modi- 

 fied prismatic cells, in which the clear 

 hardening salts are impacted, forming the 

 spiculse and fibres of enamel ; magnified 

 on the same scale as figs. 1 & 2. Fig. 5. 

 — Cement : m, primary cells ; p, their 

 granular nucleus ; n, more minutely 

 granular blastema ; n', the same, im- 

 pregnated with the ossific salts ; o, the 

 primary cell enlarged and receiving the 

 hardening salts ; p', the nucleus al- 

 tered, apparently by pressure of the sur- 

 rounding salts, and sending out prolonga- 

 tions or rays ; magnified on the same 

 scale as fig. 4. 



PLATE II. 



Magnified view of the vascular plexus of 

 the outer layer of the dental capsule 

 of the incisor of a Calf (Bos Taurus). 

 *The same, nat. size. The centre circle 

 shows the divided vessels that penetrate 

 the dentinal pulp. At two parts, a a, 

 were groups of minute capillaries, in which 

 the blood appeared to be stagnated, and 

 the vessels in progress of obliteration : 

 the cells of the capsule had begun to be 

 calcified at both these parts, and a thin 

 layer of cement to be formed. 



