IO4 



GENERAL PRINCIPLES OF ZOOLOGY. 



stituents that we see under the microscope only a homo- 

 geneous mass. The propor- 

 tion of organic and inorganic 

 substances 

 to the age 



varies according 

 and species of 

 animal: in man, for exam- 

 ple, there is 65$ inorganic to 

 35$ organic substance; in 

 the turtle, 63$ to 37^. Of 

 the inorganic constituents, 

 the most important is calcic 

 phosphate, 84$ ; in smaller 

 quantities, combinations of 

 fluoric, chloric, carbonic acids 

 and magnesia. Morphologi- 

 cally the matrix is composed 

 of the bone lamellae (Fig. 

 42), whose arrangement is 

 determined by the surfaces 

 present in and against the 

 bone. In a hollow bone 

 (like that of the upper arm 

 or of the hand) there is one 

 surface given by the external 

 border to which a fibrous, 

 skin, the bone-skin or perio- 

 steum, 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 

 course of blood-vessels. Since now the bone lamellae 

 arrange themselves parallel to the surfaces mentioned, two 

 systems may be distinguished in cross-section, the funda- 

 mental lamellae and the Haversian lamella. The former 

 are arranged parallel to the surface of the periosteum. 





FiG. 42. Cross-section through the human 

 metacarpus. a, surface of the perios- 

 teum ; ^, surface of the marrow-cavity ; 

 <:, cross-sections of the Haversian canals 

 and their system of lamellae ; d, funda- 

 mental lamellae; e, bone-corpuscles. 

 (After frey.) 



