56 



THE CONNECTIVE TISSUES 



[CII. V. 



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. 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 bone, e.g., the humerus or 

 ulna, the arrangement shown in fig. 83 can be seen. 



The bone seems mapped out into small circular districts, at or 

 about the centre of each of which is a hole, around which is an 



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



appearance as of concentric layers ; the lacunce and canaliculi follow 

 the same concentric plan of distribution around the small hole in the 

 centre, with which indeed tljey communicate. 



On making a longitudinal section, the central holes are found to 

 be simply the cut extremities of small canals which run lengthwise 

 through the bone, anastomosing with each other by lateral branches 

 (fig. 84); these canals are called Haversian canals, after the name 

 of the physician, Clopton Havers, who first accurately described 

 them. 



The Haversian canals, the average diameter of which is -^-Q of 

 an inch, contain blood-vessels, and by means of them blood is conveyed 

 to all, even the densest parts of the bone ; the minute canaliculi and 



