XXll INTRODUCTION. 



exceptiou of the Edentata, vertical folds or processes 

 of the enamel are continued into the substance of the 

 tooth, varying in number, form, extent, and direction, 

 and producing, by their superior density and resistance, 

 the ridged inequalities of the grinding surface on which 

 its efficacy in the trituration of vegetable substances 

 depends." 



Dr. Boon Hayes's thoughts are thus recorded in a 

 "Medical Circular," extracts from which appear in 

 "The Veterinarian" for 1853 (pp. 535-6): 



"In the first place, observe the pulpal cavity, which 

 is to the tooth what the medullary cavity is to bone. 

 Both originate in the same way. Into it passes an 

 artery, a vein, and a nerve. These ramify upon the 

 pulpal surface, the artery carrying blood to the denti- 

 nal tubuli, whence the liquor sanguinis (not blood 

 corpuscles) proceeds to the nourishment of this ap- 

 parently inorganic mass. 



"In the teeth of some animals this cavity seems to 

 send off diverticula between the dentinal tubuli, as if 

 for the purpose of supplying them with more vascu- 

 larity. The dentinal tubes open on the walls of the 

 pulpal cavity, and thence radiate to the enamel supe- 

 riorly and the crusta petrosa inferiorly. I think it 

 would not be difficult to prove that caries of the teeth 

 more frequently proceeds from inflammation begin- 

 ning in this cavity than from any other cause. 



"When the tubes of the dentine are examined with a 

 high magnifying power, and by transmitted light, they 

 appear dark. They are much more minute in diameter 

 than the blood globules; hence the liquor sanguinis 

 alone can penetrate them for their nourishment; so 



