HAVERSIAN CANALS. 231 



Berzelius. Middleton. 



Animal matter, . . . 33.30 33.43 



Phosphate of lime, . . . 51.04 51.11 



Carbonate of lime, . . . 11.30 10.31 



Fluoride of calcium, . . 2.00 1.99 

 Magnesia wholly or partially in the state 



of phosphates, . . 1.16 1.67 



Soda and chloride of sodium, . 1.20 1.68 



100.00 100.00 



When a bone is sawn through, it presents in some places a 

 dense and close texture like ivory, in others an open and 

 reticular texture ; hence the distinction of osseous tissue into 

 the compact and the spongy or cancellated. Both, however, 

 have the same structure, the difference being in the larger 

 interstices between the plates of bone in the cancellated form 

 in short, bony substance is everywhere porous in a greater or 

 less degree. The outer surface of a bone is always compact, 

 while the texture within is more or less spongy. 



The cancellated texture is seen on exact inspection to be 

 made up of slender bars or spiculse of bone and their lamellae 

 meeting together to form a reticular structure. The open 

 spaces or areolse of the bony network communicate together 

 freely. In the fresh state they contain marrow or blood-vessels. 

 When a long bone is broken across and its compact part is 

 examined with a magnify ing -glass, numerous little round 

 apertures are seen on the broken surface, which are the orifices 

 of short longitudinal passages running in the compact sub- 

 stance, named Haversian canals. Blood-vessels run in these 

 canals, and the widest of them also contain marrow. They 

 are from the 1000th to the 200th part of an inch in diameter. 

 They form an irregular network of tubes freely communicat- 

 ing through the compact tissue. When a thin section of 

 compact tissue is viewed under the microscope, the opening of 

 each Haversian canal is seen surrounded by concentric lamellae. 



