I HE OSSEOUS SYSTEM. 



291 



(canaliculi medullar es), are minute tubules, having an ave- 

 rage diameter of 0*01 — 0-05'", and in the extremes one 

 varying- from 0001'" to CHS'", and which, except in the 

 thinner parts of the facial bones, as above mentioned, exist 

 universally in the compact substance, forming in it a wide 

 network similar to that of the capillaries. In the long boi 

 and also in the ribs, clavicle, pubis, ischium, and lower jaw, 



Pig. no. 



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Br" 



c-- 



or 



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they run chiefly in a direction parallel to the long axis of the 

 bone, and, as shown in longitudinal sections, either parallel to 

 the surface or perpendicular to it, at distances varying from 

 O06"' to 014"' apart. They are connected by transverse or 

 oblique branches, which run in the direction both of the radius 

 and of the tangents of a transverse section of the bone. Con- 

 sequently, under a low magnifying power, in longitudinal sec- 

 Fig. 110. Segment of a transverse section from the shaft of the femur of an in- 

 dividual 18 years old, x 350 diani.: a, Haversian canals; b, their openings internally; 

 c, externally; d, osseous suhstance with lacuna;. In this figure transverse section- 

 of vascular canals and fundamental lamella? are not shown. 



