58 



THE CONNECTIVE TISSUES 



[CH. V. 



protoplasm around which the calcareous deposit is moulded ; thus the 

 dentinal tubules occupied by the processes of the odontoblasts are 

 formed. 



The other cells of the dental papilla form the cells of the pulp. 



FIQ. 72. Part of section of developing tooth of a 

 young rat, showing the mode of deposition of 

 the dentine. Highly magnified, a, Outer 

 layer of fully formed dentine ; &, uncalcified 

 matrix with one or two nodules of calcareous 

 matter near the calcified parts ; c, odonto- 

 blasts sending processes into the dentine ; 

 d, pulp; e, fusiform or wedge-shape cells 

 found between odontoblasts ; /, stellate cells 

 of pulp in fibrous connective tissue. The 

 section is stained with carmine, which colours 

 the uncalcified matrix but not the calcified 

 part. (E. A. Schiifer.) 



Formation of the enamel. 

 The portion of the enamel or 

 dental germ that covers the 

 dental papilla is at this stage 

 called the enamel organ. This 

 consists of four parts (see figs. 

 73 and 74). 



1. A layer of columnar epi- 



thelium cells in contact with the dentine. These are called 

 the enamel cells, adamantoblasts, or ameloHasts. 



2. Two or three layers of smaller polyhedral nucleated cells, the 



stratum intermedium of Hannover. 



3. A matrix of non-vascular jelly-like tissue containing stellate 



cells. 



4. An outer membrane of several layers of flattened epithelium 



cells. 



The first three layers on an enlarged scale are seen in fig. 74. 



The enamel prisms are formed by the agency of the ends of the 

 adamantoblasts which abut on the dental papilla. Each forms a fine 

 deposit of globules staining with osmic acid and resembling keratin 

 in its resistance to mineral acid. At one time it was believed that 

 ea,ch adamantoblast was itself calcified and converted into an enainej 



FIG. 73. Vertical transverse section of the 

 dental sac, pulp, etc., of a kitten, a, Dental 

 papilla or pulp ; &, the cap of dentine formed 

 upon the summit ; c, its covering of enamel ; 

 d, inner layer of epithelium of the enamel 

 organ ; e, gelatinous tissue ; /, outer epithe- 

 lial layer of the enamel organ ; g, inner layer, 

 and h, outer layer of dental sac. x 14. 

 (Thiersch.) 



