OP THE BONES. 369 



large veins, with very thin walls, which appear to consist only 

 of the inner membrane. These veins appear to have great 

 communication with the medullary cavities of the spongy sub- 

 stance. 



Lymphatic vessels are seen at the surface of the large bones 

 only. 



No other nerves are seen in the bones than those which ac- 

 company the vessels of the medullary membrane. 



586. The great hardness of the bones depends upon their 

 chemical composition. Of all the organized parts, in fact, as 

 has been seen, they contain the greatest proportion of earthy 

 substance. It must have been known all along that the bones 

 are combustible, and that they leave an earthy residuum. It 

 has also long been known that the bones furnish gelatine or 

 glue by decoction. It was Scheele who announced that the 

 earthy part of the bones is phosphate of lime. A hundred 

 parts of fresh bone are reduced to about sixty by calcination. 



According to the analysis of M. Berzelius, human bones, 

 deprived of water and fat, have the following composition: 

 animal matter reducible to gelatine by decoction, 32. 17; inso- 

 luble animal substance, 1.13; phosphate of lime, 51.4; carbo- 

 nate of lime, 11.30; fluate of lime, 2.0; phosphate of magne- 

 sia, 1.16; soda and muriate ef soda, 1.20. 



Fourcroy and M. Vauquelin, in their first trials, did not find 

 phosphate of magnesia in human bones. According to M. 

 Hildebrandt, there is none of that substance in them. Accord- 

 ing to Dr. Hatchett, there is sulphate of lime in them, which, 

 according to M. Berzelius, is a product of calcination. Lastly, 

 Fourcroy and Vauquelin admit, moreover, in the bones, iron, 

 magnesia, silica, alumina and phosphate of ammonia, but no 

 fluate. 



Besides the differences of composition dependent upon age, 

 individual constitution, and morbid affections, circumstances 

 which make the proportion of the animal substance and the 

 earthy substance vary, all the bones have not exactly the same 

 composition in the same individual. Thus the bones of the 

 skull generally contain a little more of earthy substance than 



