82 



BONE. 



On close inspection the cancellated texture is seen to be formed of 

 slender bars or spicula of bone and thin lamellae, which meet together 

 and join in a reticular manner, producing an open structure which has 

 been compared to lattice-work (cancelU), and hence the name usually 

 applied to it. In this way considerable strength is attained without 

 undue weight, and it may usually be observed that the strongest laminae 

 run through the structure in those directions in which the bone has 

 naturally to sustain the greatest pressure. The open spaces or areolaj 

 of the bony network communicate freely together ; in the fresh state 

 they contain marrow or blood-vessels, and give support to these soft 

 parts. 



Fig. 48. 



Pig. 48. — A, Transverse Section op a Bone (ulna) deprived of its earth et 



ACID. 



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

 to indicate the part magnified in Fig. B. 



B, Part of the Section A, magnified 20 diameters. 



Tlie lines indicating the concentric lamellte are seen, and among them thelacuniM appear 

 as little dark specks. 



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

 are best seen by breaking across the shaft of a long bone near its 

 middle and examining it with a common magnifying glass. Numerous 

 little round apertures (fig. 48 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 physician and writer of the seventeenth 



