HISTOLOGY OF BONE. 



89 



twenty diameters, it will be seen that numerous openings 

 exist all over the compact parts of the section and gradu- 

 ally become larger as this passes into the cancellated part, 

 next the medullary cavity. These openings are the cross- 

 sections of tubes known as the Haver sian canals, which 

 ramify all through the bone, running mainly in the direc- 



FIG 38 A a tranverse section of the ulna, natural size; showing the medul- 

 lary cavity B, the more deeply shaded part of A magnified twenty diameters. 



tion of its long axis, but united by numerous cross or ob- 

 lique branches as seen in the longitudinal section (Fig. 39). 

 The outermost ones open on the surface of the bone be- 

 neath the periosteum, and in the living bone blood-vessels 

 run from this through the Haversian canals and convey 



