84 PRACTICAL HISTOLOGY [XI 



chiefly marked off from one another by the lacunae 

 lying between them. 



Between the Haversian systems the intersystemic 

 lamellae running in various directions. 



Next the central cavity either (a) a layer of lamellae 

 which run parallel with those of the surface, or (ft) a 

 thin layer of spongy bone having rather large spaces, 

 the Haversian spaces, continuous here and there with 

 the Haversian canals on one side and the medullary 

 cavity on the other. The arrangement as regards (a) 

 and (ft) varies in different parts of the shaft and in 

 different bones. 



In the spongy bone the lamellae run in the main 

 concentric with the spaces. 



b. Examine under a high power. Observe 

 The irregularly fusiform lacunae giving off numerous 

 wavy branches, the canaliculi, which run across the 

 lamellae. The canaliculi of any one lacuna either join 

 the similar branches of neighbouring lacunce or open 

 on the free surface of the lamella. 



5. Longitudinal section of the shaft of a long bone. 

 (Prepared as in 4.) 



a. Examine with a low power. Observe 

 The Haversian canals running in the main parallel 

 with the surface of the bone, they have connecting 

 branches and open here and there on the surface and 

 into the central spaces. 



The lamellae running for the most part parallel with 

 the Haversian canals. Where a Haversian system is 

 cut obliquely the lamellae are concentric with the canal. 



