X- 



CHEMICAL COMPOSITION OF BONE 



41 



structure, and entering the medullary cavity, sends branches toward the extremities, thus 

 forming capillary plexuses in the marrow. These branches communicate with branches from 

 the periosteal vessels. The walls of the vessels are very thin; the venous blood enters the 

 spaces of the red marrow, ami the current becomes extremely slow. Small veins collect the 

 venous blood and emerge from the bone. 



FIG. 8. From a ground longitudinal section through the diaphysis of the human ulna. All canals are filled 

 with pigment, which is here black. Haversiun canals are cut longitudinally. X 90. (Szymonowicz.) 



QCfiiaS emerge from the long bones in three places: (1) One or two large veins accompany 

 the nutrient artery. (2) Numerous veins emerge at the articular extremities. (3) Manv small 

 veins ari.se in and emerge from compact substance. The latter two classes do not accompany 

 arteries. The veins in the marrow and in the bone are devoid of valves; but immediately after 

 emerging from the bone they have numerous valves. In the flat cranial bones the veins are 

 numerous and large. 



The lymphatics are chiefly periosteal; but some have been demonstrated as entering the bone, 

 along with the vessels, and running in the Haversian canals. 



Nerves, medullated (myelinic) and nonmedullated (amyelinic}, are found in bone. They are 

 distributed freely to the periosteum, and some of the fibres terminate in this structure as Pacinian 

 corpuscles. Nerves accompany the nutrient arteries into the interior of the bone, and also reach 

 the marrow from the periosteum by way of Volkmann's canals and the Haversian canals. They 

 certainly supply the arterial coats and possibly ramify about the osteoblasts. Nerves flre most 



^1111^0^ in the articular extremities of the long bones, in the vertebrae, and the large flat bones. 

 Chemical Composition of Bone. Bone consists of about 64 per cent, of animal (organic) 

 nd about 36 per cent, of earth}/ (inorganic) substance intimately combined. 

 The animal part may be obtained by immersing the bone for a considerable time in dilute 

 lineral acid, after which process the bone comes out exactly the same shape as before, but per- 

 ;ctly flexible, so that a long bone (one of the ribs, for example) can easily be tied into a knot. 

 If now a transverse section is made, the same general arrangement of the Haversian canals, 



