BOXE. 



identical. The lamellated or concentric arrangement is indeed lost and the 

 Haversian canals appear like half-tubes instead of circular spaces, and these 



Fig. 17. 



Fig. 18. 



/ , I 



A transverse section of the diaphysis of the hnme- 

 rus. (Magnified 350 times.) a, Haversian canals ; 

 b, lacunas with their canaliouli in the lamellae of 

 these canals; c, lacunae of the interstitial laraellse; 

 d, others at the surface of the Haversian systems, 

 with canaliouli going off from one side. 



Section parallel to the surface from the shaft 

 of the femur. (Magnified 100 times.) a, Ha- 

 versian canals ; b, lacunae seen from the side ; 

 c, others seen from the surface in lamellae which 

 are cut horizontally. 



tubes are seen to branch and communicate (so that each separate Haversian 

 canal runs only a short distance), but in other respects the structure has much 

 the same appearance as in transverse sections. 



In sections of thin plates of bone (as in the walls of the cells which form 

 the cancellous tissue), the Haversian canals are absent, whenever the thickness 

 of bone is not too great to allow of its nutritious juices being absorbed from 

 the fibrous membrane coating either side By means of the lacunae and canaliculi 

 only ; but when the thickness becomes, at all considerable, Haversian systems 

 begin to appear. Thus the spaces of the cancellous tissue (medullary spaces) 

 have the same function there that the Haversian canals have in the 



more 



compact tissue. 



In the long bones, by maceration in dilute mineral acid, it may easily be 

 shown that besides these microscopic lamellaa surrounding each Haversian 

 canal, the whole bone is composed of distinct laminae, concentrically disposed 

 around the medullary tube. These laminae are crossed and pinned together, as 

 it were, by the fibres of bone running obliquely through them, which were 

 first described by Dr. Sharpey, and named by him perforating fibres. In the 

 flat bones parallel or superimposed plates can be demonstrated similarly held 

 together by perforating fibres, which are more numerous than in the long bones. 1 



Besides the Haversian canals larger and irregularly shaped spaces are found 

 Haversian spaces which are as it were a transition from the Haversian canals 

 to the medullary spaces of the cancellous tissue. It seems as if both the 

 medullary spaces and the Haversian spaces are formed by absorption, as we 



Sharpey, in Qnain's Anatomy, 7th edit., p. xcvii. 



