338 



pear, are larger than any other part. All the cells of this spongy sub- 

 stance communicate with one another, they are lined by a very fine mem- 

 brane, and contain the medullary fluid. The lamina which cross each 

 other, in various directions, and which form the parietes of the cells, be- 

 come fewer in number, and thinner; the spongy tissue expands in ap- 

 proaching the middle part of the bones, and forms (within the medullary 

 canal, of the compact substance) a reticular tissue, the use of which is 

 to support the membranous tube containing the marrow. 



These three substances, notwithstanding their unequal denstiy, are, in 

 reality, but one and the same substance differently modified. The reticu- 

 lar and spongy differ from the compact, in containing less phosphate of 

 lime, and in having rarer and more expanded tissue. In other respects, 

 those changes in the osseous tissue which constitute the laminated exos- 

 toses, the conversion of the bones, by acids, into a flexible cartilage, 

 which, by maceration, may be reduced into cellular tissue, prove that these 

 three substances are truly identical, and differ from each other only by 

 the degrees of closeness of their texture and the quantity of calcareous 

 phosphate deposited in the meshes of their tissue. 



The compact substance appears to consist of concentric lamina strong- 

 ly united together, and to be formed of fibres, arranged longitudinally, 

 and in juxta position. In proof of this arrangement, it is usual to men- 

 tion the exfoliation of bones to the air; but these lamina detached from 

 an exfoliating bone, merely prove that the action of the disease, the air, 

 heat, or any other agent, by applying itself successively to the different 

 layers of bone, produces between a separation which did not exist in 

 health, and determines their falling off in succession. Certain parts, in 

 which this lamellated structure does not exist, may, in like manner, un- 

 dergo the same kind of decomposition. Thus, Lassone saw a piece of 

 human skin that had been preserved, for a considerable length of time 

 in a vault, separate into layers of extreme minuteness. 



The vital principle which exists, in a smaller degree, in the bones than 

 in other parts, seems to animate, to a certain degree, their different sub- 

 stances. Proportioned to the number of vessels which arc distributed 

 to it, life is more active in the spongy tissue; hence, in fracture of this 

 part, fleshy granulations and callus form more quickly. Caries, like- 

 wise advances more rapidly, and it is more difficult to interrupt its 

 progress. 



CLXXVII. Of the uses vf the jieriosteum and of the medullary juices. 

 Whatever be the situation, the size, the shape^ and the composition of 

 bones, they are all eveloped by the periosteum, a whitish, fibrous, dense 

 and compact membrane, to which are distributed the vessels which pe- 

 netrate into their substance. The periosteum is a membrane perfectly 

 distinct from the other soft parts, and from the bone itself, to which it 

 adheres by means of vessels and of cellular tissue, which pass from the 

 one to the other, the more closely, as we are advanced in years. The 

 cellular and vascular fibres which penetrate into the substance ofthe bone, 

 establish a very close sympathetic connexion between its periosteum and 

 the very delicate membrane that lines its internal cavity, which secretes 

 the marrow, and is called the internal periosteum. On destroying the 

 internal medullary membrane, by introducing a stylet within the cavity 

 of the bone, its external layers swell, are detached from the inner ones, 

 and form, as it were, anew bone around the sequestra. The new bone is 

 not formed by the ossification of the periosteum, as was maintained by 



