1 66 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



with the epithelium of the mucous membrane of the 

 mouth. The structure of some of these cords re- 

 sembles that of tubular glands, and Dr. Black has 

 suggested that their function may be a glandular one. 

 They not infrequently enter into the pathological 

 conditions of the peridental membrane. 



Blood Supply. Usually several small blood-vessels 

 enter the foramina at the 

 apex of the root and pass di- 

 rectly to the pulp. Upon 

 reaching the pulp these ves- 

 sels anastomose freely, form- 

 ing an extensive blood plexus. 

 A capillary plexus with nar- 

 row meshes has been de- 

 scribed between the layer of 

 odontoblasts and the dentin, 

 but does not penetrate the 

 \l * latter. Both arteries and 



lj J veins have very thin walls 



and may be easily ruptured. 

 The pulp therefore bleeds 

 very easily when exposed. 

 No accompanying lymphatics 

 have been described. 



The peridental membrane, 



being a connective-tissue layer, has a very rich blood 

 supply. Vessels enter the membrane near the apex 

 of the root, accompanying the nerve at that place; 

 small arterioles penetrate laterally from the Haver- 

 sian canals of the alveolar wall, and a third supply 

 is derived from the mucous membrane of the gum, 



Fig. 1 20. Showing the ar- 

 rangement of epithelial cords 

 or glands of the peridental 

 membrane around the root 

 of a central incisor (dia- 

 gram by Dr. Black). 



