6o 



THE CONNECTIVE TISSUES. 



[CH. V. 



part supplied with n<wrishment ; minute branches from the 

 periostea! vessels enter the little foramina on the surface of 

 the bone, and find their way to the Haversian canals, to be 

 immediately described. The long bones are supplied also by a 

 proper nutrient artery which, entering at some part of the shaft 

 so as to reach the medullary cavity, breaks up into branches for 

 the supply of the marrow, from which again small vessels are 

 distributed to the interior of the bone. Other small blood- 



Fif? 83. Transverse section of compact bony tissue (of humerus). Three of the Haversian 

 canals are seen, with their concentric rings ; also the lacunae, with the canaliculi 

 extending from them across the direction of the lamellae. The Haversian apertures 

 were filled with air and debris in grinding down the section, and therefore appear 

 black in the figure, which represents the object as viewed with transmitted light. The 

 Haversian systems are so closely packed in this section, that scarcely any interstitial 

 lamellee are visible. X 150. (Sharpey.) 



vessels pierce the articular extremities' for the supply of the 

 cancellous tissue. 



Microscopic Structure of Bone. Notwithstanding the differences 

 of arrangement just mentioned, the structure of all bone is found 

 under the microscope to be essentially the same. 



Examined with a rather high power its substance is found to 

 contain a multitude of small irregular spaces, approximately fusi- 

 form in shape, called lacunce, with very minute canals or canali- 

 culi leading from them, and anastomosing with similar little 

 prolongations from other lacunae (fig. 83). In very thin layers 

 of bone, no other canals but these may be visible ; but on 

 making a transverse section of the compact tissue as of a long 



