185 



posed of the re-union of a great number of little 

 fibres. 



In the centre of the bone is placed the marrow. 

 The spaces left between the blades are filled with a me- 

 dullary substance. 



From the thickening of the blades the growth of the 

 bone proceeds, from the lengthening of them, their 

 extending in length : all these blades grow and harden 

 after one another : each blade grows and becomes hard in 

 a like successive manner throughout its whole length. 

 That part of the blade which grows and hardens first, com- 

 poses the body of the bone, which immediately encloses 

 the marrow. This blade is again covered with a second, 

 which, being more ductile, stretches itself in a greater 

 degree. A third blade again infolds this, which, as it 

 hardens later than the others, is a longer time in its 

 growth. It is the same with respect to a fourth, fifth, 

 or sixth. As they all thus diminish in thickness, and 

 detach themselves from the axis of the bone, the nearer 

 they approach to its extremities, they form so many 

 little columns, infolded within each other, which in- 

 crease in diameter at their extremities, From hence 

 we deduce the figure peculiar to long bones. 



The growth of the bone during the first year is at- 

 tributed to the number of blades which become harden- 

 ed in that year. This bone is covered over again with 

 a great number of membraneous blades, that bear the 

 name of periosteum, which, as they gradually extend 

 and harden, conduce to the increase of the bone in every 

 part of it. The bone, when it is once formed, extends 

 itself no farther. 



Thus, in fractures t anchyloses, and the different 

 species of excrescences, whether natural or accidental, 

 the periosteum is the only part of the bone thajt labours. 

 By stretching, thickening, and swelling itself, the peri- 

 osteum restores the bone, insensibly, produces a callo- 

 sity, and forms greater or less tumors, in proportion to 

 the facility wherewith it extends itself, or as it is more 

 or less supplied with juices, or with such as are more or 

 less viscous. 



