378 THE MECHANICAL FUNCTIONS. 



we trace the branches to a certain extent, al- 

 though we cannot pursue them to their minuter 

 ramifications. They now assume more active 

 functions, and hasten to execute their task by 

 depositing granules of calcareous phosphate : 

 these are laid down, particle by particle, in a 

 certain determinate order, and in regular lines, 

 so as to form continuous fibres. When a great 

 number of these delicate fibres are gathered toge- 

 ther, and connected by other fibres, which shoot 

 in various directions across them, a texture com- 

 posed of an assemblage of long spicula, or thin 

 plates, is constituted. 



In the cylindrical bones, the spicula prevail, 

 and they are arranged longitudinally, and pa- 

 rallel to one another, and to the axis of the bone. 

 They first constitute a ring in the middle of its 

 length : this ring enlarges in all its dimensions, 

 but principally in its length ; the spicula be- 

 coming larger, not by the stretching of their 

 parts, in consequence of the insinuation of fresh 

 materials between those already deposited, but 

 by the addition of new particles at both their 

 extremities. In like manner, the ring increases 

 in thickness, not by the deposition of phosphate 

 of lime between the original layers, but by the 

 application of fresh layers on the outside of 

 those already existing. 



In the flat bones, the process of ossification is 

 very similar to what I have just described; only 



