GENERAL STRUCTURE OF THE BODY. 



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muscles. Most of the skeleton of the fetus consists of 

 cartilage, which later develops into bone. 



Bone. In bone the intercellular tissue is rendered 

 hard by the deposit of mineral salts, the resulting material 

 being of great strength and rigidity. The texture may 

 be close and dense like ivory or open and spongy, the 

 difference lying merely in the fact that the one has fewer 

 spaces between the solid particles than the other. There 

 is usually a hard, compact layer on the exterior of the 

 bone, as that is where the greatest cross-strain comes, 

 especially in the long bones, while within is the cancellous 

 or spongy tissue, which gives lightness to the bone and 

 is capable of withstanding enormous pressure, though 

 it can bear little cross-strain. 



Structure of Bone. The hard substance in bone is 

 always arranged in lamellae or bundles of bony fibers, 



Haversian canal. 



Lacuna and canaliculi. 



FIG. 4. Cross-section of compact bone tissue. (After Sharpey.) 



which in cancellous tissue meet to form a kind of lattice- 

 work, while in the dense tissue they are generally ar- 

 ranged in rings about the Haversian canals, channels 

 through which the blood-vessels pass through the bone 

 longitudinally. Between the lamellae are spaces called 

 lacunce, in which lie branched cells, the spaces being 

 connected with each other and with the Haversian 

 canals by numerous tiny canals or canaliculi, by which 

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