256 



BONE OR OSSEOUS TISSUE. 



surface, where there is a thin crust of compact substance. In the complex or mixed 

 bones, such as the vertebras, the two substances have the same general relation to 

 each other ; but the relative amount of each in different parts, as well as their special 

 arrangement in particular instances, is very various. 



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

 slender bars or spicula and thin lamellas, which meet together and join in a reticular 

 manner, producing an open structure which has been compared to lattice-work 

 (cancelli), 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 



Fig. 296. A, TRANSVERSE SECTION or A BONE (TJLNA) DEPRIVED OF ITS EARTH BY ACID (Sharpey). 



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

 the part magnified in Fig. B. 



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



The lines indicating the concentric lamellae are seen, and among them the lacuna appear as little 

 dark specks. 



strongest lamina? run through the structure in those directions in which the bone has 

 naturally to sustain the greatest pressure. The open spaces or areolas of the bony 

 network communicate freely together ; in the fresh state they contain marrow and 

 blood-vessels. 



Haversian canals. 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. 296 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 

 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^o^h to 

 aijoth of an inch in diameter : there are some no more than o^h, but these are 



