42 



THE CONNECTIVE TISSUES 



[CH. V. 



Periosteum and Nutrient Blood-vessels. The surfaces of 

 bones, except the part covered with articular cartilage, are clothed 

 by a tough, fibrous membrane, the periosteum ; and it is from the 

 blood-vessels which are distributed in this membrane, that the bones, 

 especially their more compact tissue, are in great part supplied with 

 nourishment ; 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-vessels pierce the articular extremities for the supply of the 

 cancellous tissue. 



Microscopic Structure of Bone. Notwithstanding the differ- 

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

 found under the microscope to be essentially the same. 



Fia. 55. 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 lamellae are visible, x 150. (Sharpey.) 



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 canaliculi 

 leading from them, and anastomosing with similar little prolonga- 

 tions from other lacunae (fig. 55). In very thin layers of bone, no 



