1 68 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



dentinal fibrils and the odontoblasts. The pulp is 

 very sensitive to traumatic and chemical irritations, 

 even when conveyed to it through the constituents 

 of the dentin. It is especially sensitive to changes in 

 temperature, heat or cold acting alike. It has no 

 localized sensation of touch. 



Our knowledge of the nerve supply of the periden- 

 tal membrane is not extensive. Both medullated 

 and non-medullated fibers are present, the latter 

 being a part of the sympathetic nervous system, and 

 accompany as well as innervate the small blood- 

 vessels. The nerve fibers enter the peridental mem- 

 brane in the same manner and from the same sources 

 as the blood supply, which has already been de- 

 scribed. 



Attachment of Teeth. In considering the attach- 

 ment of teeth it must be remembered that teeth are 

 not a part of the osseous system but are dermal 

 appendages. The phylogenetic history of this sub- 

 ject in vertebrates is very interesting. The de- 

 scriptive literature is extensive and many classifi- 

 cations of the different forms of attachment have 

 been made. Tomes, in his "Dental Anatomy," 

 classifies four forms of attachment: (i) by a fibrous 

 membrane; (2) hinge-joint; (3) ankylosis; (4) in- 

 sertion in a socket. 



The attachment by fibrous tissue is manifest in 

 the scaly teeth of sharks. Bach cone-shaped tooth 

 has a flattened dermal plate. Calcified connective 

 tissue is built into this plate, which it unites more or 

 less fibrously to the submucous matrix of the mouth. 

 Such teeth are practically dermal scales and have no 



