62 



STRUCTUEE OP BONE. 



by circles of little dark spots; and when these spots are 

 examined with a higher magnifying power, it is seen that 

 they are small flattened cavities, from which proceed a number 

 of extremely minute tubules (A). These tubules pass out 



a 



Fig. 17. TRANSVERSE SECTION op BONE. 



Showing the concentric rings round a a, the Haversian canals. At A are seen 

 some of the cavities with their radiating tubes, more highly magnified. 



from the two flat sides of each cavity; one set passes inwards, 

 towards the centre of the ring, and the other outwards, to- 

 wards the ring that next surrounds them. These minute 

 tubuli, which are far smaller than the smallest blood-vessels, 

 may thus be traced into every part of the substance of the 

 bone ; and those proceeding from different rings are so con- 

 nected with each other, that a communication is established 

 between the innermost and the outermost circles. The tubuli 

 which open upon the sides of the Haversian canals, are thus 

 enabled to take up the nourishment with which they are 



