74 



HANDBOOK OF PHYSIOLOGY. 



tion of the carbonate, and traces of calcium fluoride and magnesium 

 phosphate. 



Structure. Under the microscope dentine is seen to be finely chan- 

 nelled by a multitude of delicate tubes, which, by their inner ends com- 



Enamel 



Dentine. 



Periosteum 



of alveolus. 



, Cement. 



Fig. 74. Premolar tooth of cat in situ. 



municate with the pulp-cavity, and by their outer extremities come into 

 contact with the under part of the enamel and cement, and sometimes 



Fig. 75. Section of a portion of the dentine and cement from the middle of the root of an incisor 

 tootb. a, Dental tubuli ramifying and terminating, some of them in the interglobular spaces 6 and 

 c, which somewhat resemble bone lacunae ; d, inner layer of the cement with numerous closely set 

 canaliculi; e, outer layer of cement; /, lacunas; g, canaliculi. X 350. (Kolliker.) 



even penetrate them for a greater or less distance (figs. 75, 77). The 

 matrix in which these tubes lie is composed of "a reticulum of fine 

 fibres of connective tissue modified by calcification, and where that pro- 



