294 THE SOLIDS. 



ART. XV. BONE. 



THE next tissue to be considered is the osseous. 



Bones are divided after their form into long, flat, and 

 irregular : long bones consist of a body or shaft termed 

 diaphysis, hollowed out in the centre into the medullary 

 canal, and of two extremities called Epipliyses, and which 

 in early life are distinct from the shaft; each long bone, 

 moreover, is made up of two modifications of bony structure, 

 the cancellous and the tabular ; the former is loose and 

 reticular, the latter hard and compact : of the one, the great 

 bulk of the epiphyses are constituted; of the other, the 

 diaphysis is chiefly formed : in flat and irregular bones, the 

 medullary canal is wanting ; the first consist of an inner and 

 outer table of compact bony tissue, enclosing a thin plate of 

 cancellous structure, termed Diplo<z, and the latter are com- 

 posed principally of cancelli, enclosed in thin and irregular 

 osseous laminae. 



STRUCTURE OF BONES. 



The two elements into which all bones resolve themselves 

 are osseous corpuscles and lamina? ; the latter, according to 

 the plan of their arrangement and development, give rise 

 to the cancelli, medullary canals, and plates of which bones 

 are constituted. 



Cancellous Structure. 



The cancellous structure of bone is made up of thin and 

 inosculating plates of bony matter, which enclose spaces 

 between them, and all of which freely communicate with 

 each other: these spaces are called medullary cells. Each 

 plate is also compounded of several laminaa, in the intervals 

 between which a few bone corpuscles exist. 



