g NORMAL HISTOLOGY. 



of round or oval openings the Haversian canals each sur- 

 rounded by a broad band or zone composed of concentrically- 

 disposed lamellae ; the canal and the 

 FlG - 54- surrounding lamellae form an Haversian 



system. Seen in longitudinal sections, 

 the Haversian canals appear as extended 

 channels, some closely corresponding in 

 their course with the general axis of the 

 bone, while others run obliquely and es- 

 tablish free communication between the 

 adjacent canals. The concentric bone 

 lamellae in such sections appear as parallel 

 bands bordering the large channels. The 

 Haversian canals communicate with the 

 central marrow-cavity, of which they 

 are really continuations ; variable in width 

 and length, each canal contains an extension 

 of the bone-marrow, comprising a delicate 

 connective-tissue reticulum, rich in cells, 

 blood-vessels, and lymphatics. 



The areas between the Haversian systems 

 are filled out by osseous lamellae, disposed 

 without regard to the concentric systems ; these are the interstitial 

 ior ground lamellae, and represent the older parts of the bone, being 

 Ithe remains of the primaFy spongy'TTCt-work -of"pefiosteal bone. 

 ' The concentric lamellae constituting the Haversian systems are 

 secondarily deposited within the enlarged spaces of the bony reticu- 

 lum. In addition to the lamellae already mentioned, superficial os- 

 seous strata encircle the bone on 



F'G- 55- both its outer and inner (medul- 



lary) free surfaces ; these are 

 the outer and inner circum- 

 ferential or fundamental la- 

 mellae. 



Between the bundles of the 

 ground - matrix spindle - shaped 

 spaces the lacunae are seen, 

 from which minute channels the 

 canaliculi radiate in all direc- 

 tions ; these dark, stellate figures with their minute lateral canals form 

 a system of intercommunicating lymph-spaces within the bone ; the 

 canaliculi belonging to the same space or to the adjoining lacunae 

 of the same Haversian system anastomose with one another, but not 

 with the canals of different systems. 



,.! v ,'., 



Longitudinal section of dried 

 bone : h, Haversian canals opened 

 lengthwise and bordered by the 

 longitudinally-cut lamellae. 



The lacunae and canaliculi of dried bone under 

 high amplification. 



