HISTOLOGY 



105 



bones, notably the long bones of the appendages, have internal cavities 

 (Fig. 100) occupied by a more or less vascular soft tissue, the marrow. 

 The "yellow marrow" of long bones contains much fat. "Red marrow" 

 is highly vascular, contains little fat and may be a source of blood cells of 

 various types. 



In long bones the larger blood-vessels lie approximatel}- parallel to 

 the long axis of the bone. Around such vessels the bone lamellae are 

 arranged in concentric order (Figs. loi and 102) forming so-called Haver- 



FiG. 102. — Section, highly magnified, of compact bone from the shaft of the human 

 humerus. The section, cut transversely to the long axis of the bone, shows four 

 Haversian systems with their central canals, concentric lamellae of bone, lacunae 

 between adjacent lamellae, and canaliculi extending between lacunae. (From Bremer, 

 "Text-book of Histology"; after Sharpey.) 



sian systems. These concentric systems are much less prominently 

 developed in fiat bones. 



The matrix of bone consists of commingled organic and inorganic 

 materials. Collagenous and other protein substances constitute the 

 organic part while various salts of calcium, mostly the phosphate and 

 carbonate, are the most important inorganic ingredients. Bone, because 

 of the rigidity of its calcified matrix, is incapable of such interstitial growth 

 as occurs in cartilage. A further difference between cartilage and bone 

 lies in the fact that the cartilage cell produces matrix in all directions and 

 thus surrounds itself by its own product, whereas the osteoblast produces 

 matrix only at such part of its surface as is adjacent to the already- 

 formed bone. A layer of bone cells building up lamella upon lamella 



