THE CONNECTIVE TISSUES. 115 



the long axis of the Haversian canal. It is as yet undecided 

 whether the mineral salts (phosphate and carbonate of lime, sodium 

 chlorid, magnesium salts, etc.) are deposited in the ground-substance 

 (v. Ebner) or in the fibrillae (Kolliker). The lacunae (13;* to 3 1 // 

 long, 6 // to 15 //-wide, and 4 // to 9 // thick) have, in common with the 

 canaliculi, walls which present a greater resistance to the action of 

 strong acids than the rest of the solid bone-substance. In each 

 lacuna there is found a bone-cell, the nucleated body of which 

 practically fills the lacuna, while its processes extend out into the 

 canaliculi. 



The Haversian canals contain blood-vessels, either an artery or 

 a vein or both. Between the vessels and the walls of the canals 

 are perivascular spaces bounded by endothelial cells, resting on the 

 adventitious coats of the vessels and the sides of the canals. Into 

 these spaces empty the canaliculi of the Haversian system. Lymph- 

 spaces beneath the periosteum and at the periphery of the marrow 



Haversian canal. 



Fig. 84. Portion of a transversely ground disc from the shaft of a human femur; 



X40Q. 



cavity communicate directly with the canaliculi of the circumferen- 

 tial systems. 



All the lacunae and canaliculi should be thought of as filled by 

 lymph plasma which circulates throughout, bathing the bone-cells 

 and their processes. The formed elements of the lymph are prob- 

 ably too large to force their way through the very small canaliculi. 

 The plasma current probably flows from the periosteal and marrow 

 regions toward the Haversian canals. 



Between the lamellae are bundles of fibers (some of which are 

 calcified), which can be demonstrated by heating the bone, or in de- 

 calcified preparations on staining by certain methods. These are the 

 so-called fibers of Sharpey ; in the adult they contain elastic fibers. 



In the circumferential lamellae are found canals, not surrounded 

 by concentric lamellae, which convey blood-vessels from the perios- 

 teum to the Haversian canals. These are called Volkmanrf s* canals. 



The structure of bone-marrow will be discussed with the blood- 

 forming organs. 



