THE DIfiKSTIVE SYSTEM' 



241 



back through the apical foramina into the peridental membrane where 

 they unite with veins from the membrane and pass into the bone of 

 the alveolus. Enamel, cementum, and dentine are non-vascular. A 

 marked feature of the pulp vessels is the thinness of their walls, ves- 

 sels of much greater calibre than 

 are usually classed as capillaries 

 having walls of capillary thinness. 



Lymph Vessels. — Most author- 

 ities have denied the existence of 

 definite lymph channels in the 

 pulp. Schweitzer on the other 

 hand describes an arborization of 

 small lymph vessels in the pulp of 

 the crown, converging to a few 

 larger lymph vessels in the root 

 pulp and accompanying the blood- 

 vessels through the foramina of 

 the apex. 



Nerves. — The distribution of 

 nerves to the tooth follows quite 

 closely that of the blood-vessels. 

 Bundles of medullated fibres from 

 the bone at the bottom of the 

 alveolus enter the peridental mem- 

 brane just beneath the apex where 

 they divide into two main sets, 

 one of which follows the vessels of 

 the membrane while the other 

 passes with the vessels through the 

 apical foramina to the dental pulp. The membrane surrounding 

 the tooth also receives nerves from the bone of the side wall of the 

 alveolus. The branches to the pulp pass up through its center, giving 

 off branches which are mostly non-medullated and which radiate 

 toward the periphery where they form a plexus in the layer of Weil 

 just beneath the odontoblasts. From this plexus branches are given 

 off which pass in between the odontoblasts, some terminating there 

 while others end between the odontoblasts and the dentine.^ 



^Noyes calls attention to the extreme sensitiveness of dentine in spite of the fact 

 that no nerv-e fibres have been demonstrated in its canals, and believes that sensation 

 is carried to the nerve fibres through the processes (dentinal fibres) and cell bodies of 

 the odontoblasts. 

 16 



Fig, 142.- 



•Diagram of Blood-vessels of 

 Pulp. (Stowell). 



