THE CONNECTIVE TISSUES. 73 



in the arrangement of that tissue with respect to its sources of 

 nourishment. Where the bone is massed in compact form, as in 

 the shafts of the long bones, special means for supplying it with 

 nourishment is provided by a series of channels, the Haversian 



Fig. 56. 



Section of decalcified bone, parallel to axis of human femur, a, longitudinal section of 

 Haversian canal giving off transverse branch to the left; 6, tangential section of a trans- 

 verse branch ; c, lacuna occupied by bone-corpuscle ; d, intercellular substance deprived 

 of its earthy salts and so swollen that the canaliculi are obliterated. 



canals, which contain the nutrient bloodvessels, and which anasto- 

 mose with each other throughout the whole substance of the tissue. 

 The nourishing lymph, derived from the blood, reaches the cells 

 through the canaliculi and lacunae, which connect with each other 

 to form a network of minute channels and spaces pervading the 

 bone, and not only opening into the Haversian canals, but also upon 

 the external and internal surfaces of the tissue. 



In the shafts of the long bones the Haversian canals lie for the 

 most part parallel with the axis of the bone, with short transverse 

 branches connecting them with each other. It is around these lon- 

 gitudinal Haversian canals that the lamina? of bone are arranged 

 in concentric tubular layers. Each Haversian canal, with the 

 laminae surrounding it, is known as an Haversian system. Between 

 these Haversian systems there are excentric laminae of bone, which 

 do not conform to the concentric arrangement of the Haversian 

 systems. 



