162 HUMAN BONE 



transparent, according to the position of the 

 light. 



In a transverse section of bone, the lacunae 

 of the layer surrounding the Haversian canals 

 are seen to be placed tangentially to the 

 orifices of these canals, whilst those of the 

 layer near the surfaces of the bone run paral- 

 lel with those surfaces. 



A Haversian system, consisting of a Ha- 

 versian canal, its lacunae, and all the canali- 

 culae that communicate with that same canal, 

 is complete in itself, and entirely independent 

 of other Haversian systems. 



Chemically, bone consists of gelatine with 

 phosphate of lime and magnesia, small quan- 

 tities of carbonate of lime, carbonate of mag- 

 nesia, fluoride of calcium, and a little oxide 

 of iron and magnesia. 



The photo-micrograph from which the illus- 

 tration (Fig. 49) was taken shows an ampli- 

 fication of 550 diameters the Haversian canals 

 appearing as large as chestnuts; the objective 

 used was the one-sixth, and the focal distance 

 was 78 inches. 



