144 GENERAL ANATOMY. 



membrane, in the cartilages: at a later period, the cavity of 

 the large bones is merely a narrow canal filled by the artery; 

 when the canal begins to enlarge, the artery throws itself on 

 the side, and fastens itself to the parietes; a viscid or gelatinous 

 substance is then contained in the canal; marrow is finally pro- 

 duced in it, but in small quantities ; in time, the canal increases 

 in size, and the marrow becomes more abundant. As respects 

 this tissue, there is no perceptible difference between the 

 sexes. This fluid, presents individual differences as relates to 

 quantity. In a state of ordinary plumpness, fat forms the 

 greater part of the substance contained in the medullary canal. 

 In eight parts of this substance, I have found seven of fat : the 

 remainder is formed by the vessels, water and albumen. In 

 lean subjects, on the contrary, the fat constitutes only a fourth, 

 or even a less proportion of the fluid contained in the long 

 bones : the remainder appears to me to be water, or at any rate 

 an evaporable substance, and albumen, or a coagulable sub- 

 stance. According to Camper, there is air, instead of marrow 

 in the cavities of the long bones of birds. 



178. The functions of the medullary tissue, are to serve as 

 an internal periosteum, and as a reservoir for the fat: it is upon 

 it that those vessels ramify, which are directed outwards on 

 the one hand, to assist in nourishing the bone, and inwards, 

 on the other, to produce the secretion of the fat. The latter, 

 has the same uses as in other parts. Its local use is to fill up 

 those spaces which without it would exist in the bones. It 

 has been thought, and Haller and Blumenbach were of the 

 opinion, that it rendered the latter more flexible, and less fran- 

 gible; but the bones of children, deprived of fat, are, however, 

 less frangible than those of adults, while the bones of old peo- 

 ple, in whom this fluid is so very abundant, are in general very 

 fragile. Those who have advanced this opinion, found it upon 

 the fact, that combustion deprives the bony substance of all its 

 solidity; it is evident, however, that in this case it is not the 

 oil only which it loses, but the animal matter also, on which 

 depended their solidity. The same authors add, that by boil- 

 ing the earthy residuum, obtained by the combustion, in oil 

 or gelatine, its solidity, to a certain degree, is restored; but a 



