268 



STUDIES IN ADVANCED PHYSIOLOGY. 



the tooth is made of a substance known as dentine, or ivory. 

 In composition it is not very different from bone, but his- 

 tologically it is not the same. Dentine possesses neither 

 Haversian canals nor lacunae, and so, of course, has no 

 osteoblasts imbedded in its substance. Running, however, 

 from the pulp cavity outward and permeating the dentine 

 everywhere are fine tubules, each about Toinr of an inch 

 in diameter. Near the outside of the dentine these tubules 

 frequently open into large irregular spaces known as inter- 

 globular spaces. The function of these spaces is not known. 



Fig. 101. SECTION OF FANG OF HUMAN CANINE. (After Waldeyer.) 

 1, cement, with lacunae and lamellae; 2, layer of interglobular spaces; 3, dentinal 



tubules. 



Through these dentinal tubules, for a little distance at least, 

 arms of dentinoblasts extend, which are immediately con- 

 cerned with the growth and repair of the dentine. These 



