SIXTH LECTURE. 



BONE TISSUE. 



We now turn to the most complicated variety of connective 

 substance : we refer to the osteoid or bone tissue. 



It is distinguished for its considerable hardness and firm- 

 ness. In man, this member of our tissue group is, with the 

 exception of a covering to the tooth root, limited exclusively 

 to the bones. 



The anatomists divide the latter into long or cylindrical, 

 broad or flat, and, finally, short or irregular bones. 



Let us begin with the middle portion or diaphysis of the 



former, taking a radial longi- 

 tudinal section sawn out from 

 the dry femur (Fig. 58). 



A very peculiar appear- 

 ance is presented. The thin 

 lamella is permeated by a 

 system of longitudinal ca'nals, 

 connected, in a reticular man- 

 ner, with a medium width of 

 O.i 128 to 0.0149 mm. (a). 

 The transverse branches open 

 out onto the surface of the 

 bone, as well as inwards into 

 the medullary canals, and re- 

 ceive the nutrient vessels 

 from both sides. They bear 

 the name of the medullary 

 or Haversian canaliculi. 

 Tr; nsverse sections (Fig. 59) naturally present an entirely 

 different appearance. The rounded and oblique spaces (c) 



-«H«' \--ii 



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mum 





Fig. 58. — Vertical section through the human 

 femur; a, medullary canals ; b, bone corpuscles. 



