166 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 

 latter. Both arteries and 

 veins have very thin walls 

 and may be easily ruptured. 

 The pulp therefore bleeds 

 very easily when exposed. 

 No accompany ing 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. 120. 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). 



