THE TEETH 325 



so that if this tissue is forcibly separated from the dentin the odonto- 

 hlasts remain adherent to the connective tissue of the pulp. The nuclei 

 of the odontoblasts are found near their inner or basal extremity. Their 



v 



cytoplasm is of considerable extent as compared with that of the other 

 connective tissue cells of the pulp. 



The dental pulp is richly supplied with blood-vessels, derived from 

 a nutrient artery which enters through the root canal, its several 

 branches forming a network of minute arterioles and capillary vessels 

 in the center of the pulp cavity, and a peripheral close-meshed capil- 



FIG. 305. FROM A SECTION OF A HUMAN TOOTH WHICH HAD BEEN GROUND TO 



EXTREME THINNESS. 



a, dentin; 6, granular layer of Tomes; c, enamel. Photo. X 150. 



lary network which is in close relation with the layer of odontoblasts. 

 Numerous delicate lymphatic vessels, uniting to leave the root as one 

 or several large vessels, have also recently been demonstrated in the tissue 

 of the dental pulp (Schweitzer). 



A rich nerve supply is derived from fine branches which also enter 

 by the root canal. Most of the nerve fibers lose their myelin sheaths 

 soon after they enter the pulp. They form a primary plexus in the 

 connective tissue from which fine fibers pass to the periphery and 

 form a marginal plexus beneath the odontoblasts. From here delicate 

 terminal sensory fibrils ramify over the odontoblasts and pass in great 

 abundance into the dentinal tubules, usually two to each tubule (Mum- 

 mery, Proc. R. Soc., Series B, 85, 1912). This peripheral distribution 

 of nerve fibrils explains the extreme sensitiveness of the dentin. Sympa- 

 thetic fibers supply the muscle cells of the pulp arterioles. 



Dentin. The dentin surrounds the entire pulp cavity except at 

 the opening of the root canal. It is a fine calcareous substance which 

 resembles bone in that it consists of a collagenous fibrous matrix and 

 is infiltrated with lime salts. The matrix is a fine fibrous network of 



