380 



THE TISSUES. 



Fig. 241. 



and slightly hardened, the whole appears to consist of isolated glo- 

 bules. Some of them are also visible at later periods, the spaces 

 between them being the interglobular spaces already described (p. 

 370). Usually, however, these spaces are filled by a deposition of 

 dentine also, so that the latter becomes quite homogeneous and clear. 

 2. The enamel-cavity is a closed sac, and contains the enamel-pulp, 

 which is applied to the dentinal pulp like a cap, and presents a pe- 

 culiar structure. 1. Its mass consists 

 at first of anastomosing stellate cells 

 (Fig. 239), containing a great quantity 

 of fluid, rich in albumen (and mucus, 

 Kolliker\ in its meshes. It forms a 

 layer ^ to ^ of an inch thick in the 

 foetus of five or six months, and but 

 ?V to 5 ! o f an i QC h at birth ; when it 

 contains vessels in its outer third, and 

 its network is metamorphosed into 

 white fibrous tissue. 2. On the inside, 

 however, of this spongy tissue lies a 

 true cylindrical (conoidal) epithelium 

 in contact with the dentinal pulp. This 

 is incorrectly termed the enamel-raera- 

 brane (membrana adamantinse, Rasch- 

 kow). Its cells are y^ 1 ^ of an inch in 

 length, and g^^ of an inch in breadth, 

 are finely granular, and their nuclei 

 are frequently situated at their extre- 

 mities. 



The enamel-fibres are formed by the 

 complete and direct ossification of the 

 cells just mentioned, without a pre- 

 vious deposit of calcareous matter in a 

 granular form. (KoUiker.) (Fig. 241.) 

 The first layer of enamel is deposited 

 upon the outermost layer of dentine, 

 already described, and the successive 

 ones are formed externally to this, till 

 the required thickness is obtained. 

 Meantime the epithelial layer %con- 

 stantly remains of the same thickness 



Formation of enamel, h. Primarj 

 cells suspended in fluid blastema, g, i. 

 The same more fully developed, and be- 

 come angular, j. The same becoming 

 prismatic, k. The nucleus disappear- 

 ing. I. The modified prismatic cells 

 filled with calcareous salts, forming the 

 fibres of enamel. 



