BONE. 



municate freely together ; in the fresh state they contain marrow or blood- 

 vessels, and give support to these soft parts. 







Fig. XLIII. A, TRANSVERSE SECTION OP A BOICE (ULNA) DEPRIVED OF ITS EARTH BY 



AOID. 



The openings of the Haversian canals seen. Natural size. A small portion is shaded 

 to indicate the part magnified in Fig. B. 



B, PART OF THE SECTION A, MAGNIFIED 20 DIAMETERS. 



The lines indicating the concentric lamellae are seen, and among them the corpuscles or 

 lacuiise appear as little dark specks. 



The compact tissue is also full of holes ; these, which are very small, are 

 best seen by brtaking across the shaft of .a long bone near its middle, and 

 examining it with a common magnifying glass. Numerous little round 

 apertures (fig. XLIII. A) may then be seen on the broken surface, which are the 

 openings of short longitudinal passages running in the compact substance, 

 and named the Haversian canals, after Clopton Havers, an English physi- 

 cian and writer of the seventeenth century, who more especially called 

 attention to them. Blood-vessels run in these canals, and the widest of 

 them also contain marrow. They are from T ^ 5 th to ^^th ^ an " lcn * n 

 diameter : I have measured some which were no more than ^-^ g ^th, but 



these are rare ; the medium size is about ^ Jo tn - The widest are those 

 nearest the medullary cavity, and they are much smaller towards the cir- 

 cumference of the bone. They are quite short, as may be seen in a longi- 

 tudinal section, and somewhat crooked or oblique at their ends, where they 



