GENERAL HISTOLOGY. 



87 



glutin, so intimately combined with inorganic constituents that it 

 appears under the microscope as 

 a homogeneous mass. The propor- 

 tion of organic and inorganic sub- 

 stances varies according to the age 

 and species of animal : in man, for 

 example, there is 65$ inorganic to 

 35$ organic substance; in the 

 turtle, 63$ to 37$. Of the in- 

 organic constituents, the most im- 

 portant is calcic phosphate, 84$; 

 in smaller quantities, combinations 

 of fluoric, chloric, carbonic acids 

 and magnesia. Morphologically 

 the matrix is composed of the bone 

 lamellae (fig. 44), whose arrange- 

 ment is determined by the surfaces 

 present in and upon the bone. In 

 a hollow bone (like that of the 

 upper arm or of the hand) there is 

 an outer surface to which a fibrous 

 skin, the bone-skin or periosteum, 

 is closely applied; the presence of 

 the marrow-cavity necessitates a 

 second surface. Finally, the solid 

 mass of the bone is permeated by 

 the Haversian canals, which run 

 chiefly in a longitudinal direction, 

 united into a network by cross or 

 oblique canals, and serve for the 

 passage of blood-vessels. Since the 

 bone lamellae arrange themselves 

 parallel to the surfaces mentioned, two systems may be distin- 

 guished in cross-section, the fundamental lamellae and the 

 Haversian lamellae. The former are arranged parallel to the sur- 

 face of the periosteum and of the marrow-cavity and form a 

 mantle of concentric layers around the marrow-cavity. Into this 

 groundwork the Haversian canals with their lamellae enter, 

 destroying and superseding the fundamental lamellae coming in 

 their way. The Haversian lamellae are concentrically arranged 

 around the lumen of the Haversian canals just as the fundamental 

 lamellae are around the marrow-cavity. 



FIG. 44. Cross-section through the 

 human metacarpus. (After Frey.) a, 

 surface of the periosteum; 7>, surface 

 of the marrow-cavity; c, cross-sec- 

 tions of the Haversian canals and 

 their system of lamellae; d, funda- 

 mental lamellae; e, bone corpuscles. 



