368 GENERAL ANATOMY. 



viewing the tissue of the bones as an areolar organic tissue 

 like the others, but containing earthy substance in extremely 

 narrow cavities, much in the same manner as water is inter- 

 posed in the tissue of a moist sponge. Others consider the 

 bone as an intimate mixture or a combination of gelatine and 

 phosphate of lime. Mascagni regards it as formed of absorb- 

 ent vessels filled with phosphate of lime. These hypotheses 

 however, do not rest upon any fact, or rather are in contra- 

 diction to facts. At the same time it is not known in what 

 exact proportion the earthy substance exists to the organic 

 substance of the bones. 



585. Some tissues belong essentially to the organization of 

 the bones: these are the periosteum, the marrow, and the 

 vessels. y>*. 



The periosteum is a very vascular fibrous membrane which 

 envelops the bone, as has already been seen (522.) 



The medullary membrane is a very vascular cellular mem- 

 brane, which contains the marrow, and serves as an internal 

 periosteum to the bones (169 178.) 



The blood-vessels of the bones, which are pretty numerous, 

 and of different volume, are distinguished into those which 

 first ramify in the outer periosteum, and then penetrate into 

 the small nutritious foramina of the compact substance; those 

 which penetrate, without ramifying, into the medullary canal, 

 where they are distributed to the membrane of that name, 

 and then penetrate through the inner surface into the compact 

 substance, where they communicate with the preceding; and, 

 lastly, into those which penetrate through the large and nu- 

 merous foramina of the short bones and spongy parts of the 

 long and broad bones, to be distributed in the spongy substance, 

 % and communicate there, in the long bones, with the vessels 

 of the two first orders. Some anatomists have given the names 

 of nutritious vessels of the first order to those of the medullary 

 canal of the long bones ; nutritious vessels of the second order, 

 to those of the spongy part; and of the third order, to those 

 which pass from the outer periosteum into the compact sub- 

 stance. In general, each of the nutritious canals contains an 

 artery and a vein. Those of the second order contain very 



