THE DEVELOPMENT OF THE TEETH. 167 



by their calcification that bone or cementum is directly 

 formed. These osteoblasts are themselves a special de- 

 velopment where bone is about to be manufactured, as is 

 clearly explained in the following extract from a paper by 

 my father and the late Mr. De Morgan, who termed them 

 osteal cells : 



" Here (towards the bone) in the place of cells with 

 elongated processes, or cells arranged in fibre-like lines, we 

 find cells aggregated into a mass, and so closely packed as to 

 leave little room for intermediate tissue. The cells appear 

 to have increased in size at the cost of the processes which 

 existed at an earlier stage, and formed a bond of union be- 

 tween them. Everywhere about groiving bone a careful ex- 

 amination ivill reveal cells attached to its surface, while the 

 surface of the bone itself ivill present a series of similar bodies 

 ossified. To these we propose to give the name of osteal 

 cells, as distinguished from lacunal and other cells." 



Externally to the osteoblast layer, but still very near to 

 the perfect cementum, lies a reticulum or network made up 

 by the inosculating branches of cells. The cells have largish 

 round nuclei, and are each furnished with three or four homo- 

 geneous processes, so that the tissue, save in very thin sec- 

 tions, looks hopelessly confused from the interlacing of the 

 cell processes. Many of these processes pass into, and are lost 

 in the clear, structureless matrix of the already formed 

 cementum ; the functions which they perform in its deve- 

 lopment are not very apparent, as they do not correspond 

 to anything which can be traced in the completed tissue. 



Externally to the fine-meshed net-work which has been 

 well figured and described by Dr. Lionel Beale, the soft 

 tissue surrounding the root partakes more of the character 

 of ordinary fibrous tissue, and may be teased out into 

 fibrils. The fibrous bands run mainly in a direction from 

 the alveolus towards the tooth. Many of them pass through 

 the whole thickness of the soft structures, extending from the 



