THE SUPPORTING TISSUES. 91 



canaliculi and come in contact with similar arms of neigh- 

 boring osteoblasts. In this way there is really a system of 

 direct communication between the living parts of the entire 



Fig. 42. AN OSTEOBLAST IN DETAIL. 



o, the wall of the lacuna where the bone corpuscle has shrunk away from it. 



v bone. These osteoblasts are the agents which secrete the 

 bone substance surrounding them, somewhat like the clam 

 secretes its surrounding calcareous shell. The bone sub- 

 stance, or the matrix, as it is called, appears perfectly 

 homogeneous, but with proper reagents there may be 

 brought to view many little fibres permeating it in all 

 directions. These fibres, no doubt, add materially to the 

 strength and consistency of the bone, somewhat as the 

 hairs frequently mixed with mortar materially serve to keep 

 that from crumbling. These fibres were named after the 

 person who first carefully described them, and called the 

 fibres of Sharpey. The firmness of the matrix is due to the 

 large amount of mineral matter which it contains, there 

 being about sixty-five per cent, of inorganic matter in bone. 

 Of these inorganic constituents the most abundant is cal- 

 cium phosphate. In small quantities there occur combina- 

 tions of fluorine, chlorine and magnesia. Small quantities 

 of calcium carbonate are present. In this matrix the osteo- 

 blasts are not merely included by chance, but remain there 

 in order to look after the constant wear and repair of the 

 osseus tissue. By extracting the proper ingredients from 

 the lymph which seeps to them, they are enabled wherever 

 either the cell itself or its arms touch, to secrete new bone, 



