OSSEOUS TISSUE. 



327 



cellus, whose walls are formed of laminae of osseous tissue. These 

 cavities are quite irregular in form, and communicate freely with 

 each other, as may be seen in a section of the short bones, or of the 

 extremities (epiphyses) of the long ones. Indeed, their appearance 

 is so similar to the areolas of the sponge, that the terms spongy, 

 areolar, or reticulated bone-structure are also applied to them. 



The walls of the cancelli are formed of several concentric laminae 

 of osseous tissue, between and in the substance of which lacuna 

 and pores exist ; and through an opening the vessels are sent into 

 the cavity of the cancellus, to ramify upon its inner surface. If the 

 cancellus be supposed, for the sake of simplicity, to assume a sphe- 

 rical form, its appearance on section will be represented by Fig. 215. 



Fig. 216. 



Appearance of cancelli while developing. 

 At A, the section is made near the surface of 

 ossification ; at B, more distant, and showing 

 the cancelli with thicker walls. The new 

 osseous lining is transparent, and appears 

 light in both figures. The cancelli are filled 

 with debris, from grinding the preparation. 

 A, in Fig. B, shows where a bony partition 

 has been broken away. 



The cancelli, however, in fact, communicate so freely with each 

 other, that their walls lose the structural regularity there represented ; 



