BONE. 65 



cesses as were formerly believed to exist it having 

 been shown that some, at least, if not all, of the sup- 

 posed processes are really portions of the intercellular 

 substance lining the lacunae and canaliculi. In young 

 bone the cells are not flat, but spherical or ovoidal. 



We distinguish two kinds of bone-tissue, spongy 

 and compact. 



In spongy bone-tissue, which is found in abundance 

 in the epiphyses of the long bones, the hard sub- 

 stance, or bone proper, is arranged in the form of 

 thin plates, which are grouped together so as to 

 enclose tiny, irregular-shaped cavities, filled with 

 marrow-tissue. In these thin plates of spongy 

 bone the cells lie irregularly scattered through the 

 intercellular substance, which is homogeneous. 



In compact bone, such as is found in the diaphyses 

 of the long bones, the intercellular substance is ar- 

 ranged in layers, or lamellae, in and between which 

 lie the cells. The lamellar arrangement is best seen 

 in transverse sections from the diaphyses of the long 

 bones. If we look at a thin cross-section of such a 

 bone with a low magnifying power, we notice nu- 

 merous round, or ovoid, or irregular-shaped open- 

 ings, of varying size, and around these are grouped 

 several thin concentric layers of basement substance, 

 in and between which lie. the cells, flattened in the 

 plane of the lamellae. 



These sets of concentric lamellae are called special 

 or Haversian systems of lamella. Sometimes these 

 5 



