234 



COMPARATIVE ZOOLOGY 



FIG. 204. Transverse section of a Bone (Human 

 Femur), x 50, showing Haversian canals. 



(4) Osseous Tissue. This hard, opaque tissue, called 

 bone, differs from the former two in having the inter- 

 cellular spaces or 

 meshes filled with 

 phosphate of lime 

 and other earths, in- 

 stead of a hyaline or 

 fibrous substance. It 

 may be called pet- 

 rified tissue the 

 quantity of earthy 

 matter, and therefore 

 the brittleness of the 

 bone, increasing with 

 the age of the animal. 

 If a chicken bone be 

 left in dilute muriatic acid several days, it may be tied 

 into a knot, since the acid has dissolved the lime, leav- 

 ing nothing but cartilage and connective tissue. If a 

 bone be burned, it be- 

 comes light, porous, 

 and brittle, the lime 

 alone remaining. 71 



Bone is a very vas- 

 cular tissue; that is, 

 it is traversed by 

 minute blood vessels 

 and nerves, which 

 pass through a net- 

 work of tubes, called 

 Haversian canals. 



The Canals average FjG 2Q5 _ Fronta i Bone of Human Skull under the 

 __.!_._ Q g^ inch be- microscrope, showing lacunae and canaliculi. 



ing finest near the surface of the bone, and larger 

 farther in, where they form a cancellated or spongy 





