136 



NORMAL HISTOLOGY. 



Dentine 



is often applied to this part of the periosteum, which lines the alveoli, on the 

 one hand, and covers the cementum on the other and thereby fulfils the 

 double role of periosteum and root-membrane. The alveolar periosteum is 

 made up of tough bundles of fibrous tissue, elastic fibres being almost want- 

 ing, which are prolonged as the penetrating fibres into the cementum, on 

 one side, and as the fibres of Sharpey into the alveolar wall, on the other. 

 In the upper part of the root, the fibrous bundles are almost horizontal, but 

 towards the apex they are more oblique, the periosteum here losing its dense 

 character and becoming a loose connective tissue through which the blood- 

 vessels and nerves pass to the root-canal on their way to the pulp. At the 

 alveolar border the pericementum is directly continuous with the stroma of 

 the gum and immediately beneath the border of the enamel the fibrous bun- 

 dles are consolidated into a dense band, the ligamentum circulare dcntis, 

 which still further aids in maintaining the firm union between the tooth and 



the alveolar wall. In addition to 

 blood-vessels and nerves, within the 

 pericementum lie irregular groups 

 of epithelial cells, which appear as 

 cords or networks within the con- 

 nective tissue stroma. The groups 

 are the remains of the enamel-sheath 

 (page 140), which surrounded the 

 young tooth during its early devel- 

 opment, and have been mistaken 

 for glands. 



The Pulp. The contents of 

 the pulp-cavity is the modified meso- 

 dermic tissue of the dental papilla 

 remaining after the formation of the 

 dentine. The adult pulp consists 

 chiefly of soft highly vascular con- 

 nective tissue, containing few or no 

 elastic fibres but many irregularly 

 distributed cells. The general type 

 of the tissue resembles embryonal, 

 both in its fibrous tissue and in its 

 cells, the latter being round, oval or 

 stellate with long processes. The peripheral zone of the pulp, next the den- 

 tine, is of especial interest, since in this situation lie the direct descendants 

 of the dentine-producing cells, the odontoblasts. These are tall columnar 

 cells, arranged vertically to the surface of the pulp, about 25 p. in length and 

 5 At in breadth, which send out long delicate processes, the dentinal fibre s, 

 into the dentinal tubules and short ones into the pulp-tissue. The spaces 

 between the bases of the odontoblasts are occupied by smaller cells, less 

 regularly disposed and less cylindrical and more uncertain in form. 



The blood-vessels supplying the pulp are from three to ten small 

 arteries which break up into capillary networks soon after entering the pulp- 

 cavity. In human teeth the capillaries usually do not invade the layer of 

 odontoblasts. The larger. veins, formed by thin-walled radicles, follow the 

 general course of the arteries. Lymphatics have been recently demon- 

 strated within the pulp as networks. The nerves supplying the pulp-tissue 

 are numerous, each fang receiving a main stem and several additional smaller 

 twigs, which in a general way accompany the blood-vessels. They include 



Pulp- 

 tissue 



Blood- 

 vessel 



FIG. 176. Section of periphery of pulp-tissue of young 

 tooth. X 175. 



