294 MICROSCOPIC ANATOMY OF THE TEETH 



Smith calls abrachiate lacunae. The incremental lines in 

 cement follow the contour of the root and form the 

 laminse in thick cement ; they are, as in bone, the indica- 

 tion of the incremental deposit of the calcined tissue, and 

 have been known as ' the incremental lines of Salter '. 



Development of Cement. In the cement of human teeth, 

 which is confined to the roots, the process of ossification is 

 exactly similar to that of bone in membrane. In ungulates 

 and animals possessing coronal cement, a cement organ has 



FIG. 188. Feathery canaliculi in cement in root of 

 human molar. ( x 150.) 



been described by Robin and Magitot (6). They say : 

 ' The coronary cement is produced by the mode of ossifica- 

 tion, called ossification by substitution, or by the ossification 

 of preceding cartilage of the same form, for which is sub- 

 stituted a corresponding osseous layer.' The details of the 

 process of ossification given by these authors do not, how- 

 ever, exactly correspond to those of the ossification of bone 

 in cartilage generally accepted. They describe the invasion 

 of the fibre-cartilaginous basis substance by points or spots 

 of ossification which form small plates produced into pro- 

 longations or trabeculee which arise from their periphery, 



