152 



THE ESSENTIALS OF HISTOLOGY. 



a granular appearance (granular layer, fig. 175, 2), and also in the 

 course of certain lines or clefts which are seen traversing the dentine 

 across the direction of the tubules (incremental lines, fig. 172, shown 

 magnified in fig. 177). The dentine can be separated into lamellae 

 along these incremental lines. 



The animal matter of dentine resembles bone and the connective 

 tissues generally in having its ground substance pervaded by fibres 

 which yield gelatine on boiling. These fibres, which have been 

 especially investigated by v. Ebner and by Mummery, are difficult of 

 demonstration in the fully calcified dentine ; but in developing 

 dentine and in dentine which is attacked by caries they are more 

 easily shown. 



FlG. 177. A SMALL PORTION OF DENTINE WITH 1NTERGLOBULAR SPACES. 



(Kolliker.) (350 diameters.) 



c, portion of incremental line formed by the interglobular spaces, which are here filled up 

 by a transparent material. 



The pulp consists of a soft, somewhat jelly-like, connective tissue, 

 containing many branched cells, a network of blood-vessels, and some 

 nerve-fibres which pass into the pulp-cavity along with the blood- 

 vessels by a minute canal at the apex of the fang. The superficial 

 cells of the pulp form an almost continuous layer, like an epithelium. 

 They are known as odontoblasis, from having been concerned in the 

 formation of the dentine. 



The crusta petrosa ;(fig. 175, 1) is a layer of lamellated bone in- 

 cluding lacunae and canaliculi, but without Haversian canals, at least 

 normally in the human teeth. It is covered with periosteum (dental 

 periosteum), which also lines the socket, and serves to fix the tooth 

 securely. 



Formation of the teeth. The teeth are developed in the same 

 manner as the hairs. A thickening of the epithelium occurs along the 

 line of the gums, and grows into the corium of the mucous membrane 





