DIGESTIVE SYSTEM. 167 



vessels passing over the border of the alveolar proc- 

 esses. This vascular condition is important, both in 

 health and disease. 



Nerve Supply. The tooth pulp is supplied with 

 nerve fibers from the fifth cranial nerve. Medul- 

 lated dendrites of sensory neurons enter the pulp 

 cavity through the apical foramen of the root. All 

 of them lose the medullary sheath, but do so at 

 variable distances in the pulp. The varicose den- 



- Odonto- 

 Odontoblasts. 



Fig. 121. Nerve termination in the pulp of a rabbit's molar, 

 stained in methylene-blue (intra vitam): a, Odontoblasts seen in side 

 view; b, a number of odontoblasts seen in end view, showing a termi- 

 nal branch of a nerve fiber situated between the odontoblasts and the 

 dentin (Huber). 



drites ultimately form a loose plexus immediately 

 under the layer of odontoblasts and, therefore, 

 practically at the periphery of the pulp. Small 

 branches pass from this plexus to terminate between 

 the odontoblast cells, or pass through the layer of 

 odontoblasts, but in no case have they been traced 

 into the dentin. The sensitive dentin is, therefore, 

 due to an indirect irritation of these nerve endings, 

 conveyed to the latter through the medium of the 



