THE STRUCTURE AND ECONOMY OF BONE. 65 



which it is isolated, divided into small portions, and concealed in 

 the cavities of the osseous corpuscules. 



The hard part of the osseous texture, considered in a long 

 bone, presents four surfaces, all communicating with one an- 

 other, a periosteal or external, a medullary or internal, a haver- 

 sian or intermediary, and a corpuscular or canalicular. The peri- 

 osteal surface communicates with the haversian in three ways : by 

 those haversian canals which open in it ; by the canal for the 

 medullary artery gradually subdividing and diminishing till it 

 breaks up into arterial haversian canals ; and by the more numer- 

 ous canals for the veins, principally met with at the extremities 

 of the bone. The medullary surface is to be considered as a 

 portion of the haversian, having been formed by the enlargement, 

 and subsequent blending of neighbouring haversian canals into 

 medullary cavities and cancelli. The canalicular or corpuscular 

 surface forms the walls of the innumerable corpuscules and cana- 

 liculi, and communicates by the latter with the haversian, me- 

 dullary, and less freely with the periosteal surface. 



The compact osseous substance, in which the corpuscules and 

 then: canaliculi are situated, is not homogenious in texture* It 

 consists, of cells filled with bony substance, ossified or calcified 

 primordial cells. 



The soft part of the true osseous texture is not continuous like 

 the hard, but is divided, as has been stated, into as many portions 

 as there are corpuscules in the bone. Each of these portions 

 consists of a little mass of nucleated cells of great transparency. 

 They do not appear to extend along the canaliculi, but to be con- 

 fined to the cavity of the corpuscule* 



These two parts, the hard and the soft combined, constitute the 

 true osseous texture. They differ from one another only in this, 

 that the cells of the one are ossified, those of the other retain their 

 original delicacy and softness. The masses of soft cells in the cor- 

 puscules, I am inclined to consider as the nutritive centres, germi- 

 nal centres, or germinal spots of the texture. These centres are 

 the source of all the hardened cells, each of them being the centre 

 of all those comprehended within the range of its own canaliculi. 

 Each of these soft germinal masses is the centre of attraction 

 for the proper nutriment of bone, and is the active agent in with- 



