56 



THE TISSUES. 



Bone (Fig. 25) is another specialized form of connective 

 tissue, made up of bone-cells or corpuscles and an intercellular 

 matrix impregnated with calcareous salts. It occurs in two 

 forms, compact, making up the greater part of long bones and 

 the outer part of all bones, dense and solid ; and cancellous, in 

 the ends and lining the medullary canal of long bones and in 

 the interior of all other bones ; it is loose and spongy, consisting 

 of spaces (cancelli) separated by thin osseous walls. 



The material of which bone is composed is divisible into 

 two kinds, organic and mineral. By burning, the organic 

 portion is destroyed, leaving the mineral portion ; while on 



FIG. 25. 



Cross-section of compact bone, showing Hayersian systems, bony lamellae, 

 lacunae, and canaliculi (Klein). 



treatment with acid the mineral matter is removed, or the 

 bone is " decalcified," the organic material remaining as a 

 tough flexible substance. 



The bone-cells are modified connective-tissue cells, of a 

 flattened shape, with numerous fine processes projecting from 

 them in all directions. The bodies of the cells occupy the 

 spaces called the lacunce, while the processes occupy the 

 canaliculi. 



The matrix consists of dense fibrous organic matter (such as 

 appears in decalcified bone) impregnated with calcareous salts. 

 It is arranged in series of concentric lamella 1 , which form four 



