160 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



the root portion of a tooth. At the gingival margin 

 it slightly overlaps the enamel. Near this margin it 

 forms a thin layer, but becomes thicker toward the 

 apex of the root and between the roots of the bi- 

 cuspids and molars. The cementum consists of 

 parallel lamellae of bone tissue that contain no 

 Haversian canals. Small blood-vessels from the in- 

 vesting peridental membrane penetrate the lamellae, 

 while other small vessels from the pulp pass through 



Fig. 117. Cross section of human tooth, showing cement and dentin. 

 At a are seen small interglobular spaces (Tomes' granular layer). 



the cementum in the opposite direction. Fibers 

 from the investing peridental membrane find attach- 

 ment in the cementum. These fibers resemble the 

 fibers of Sharpey in bone. The cementum, there- 

 fore, furnishes a medium of attachment by which the 

 tooth is held in position. 



Cementum is constantly being produced by the 

 apposition of new surface layers. In newly erupted 



