CERTAIN TISSUBS. 



607 



sian canals), while the intermediate space is occupied by cavir 

 ties (lacunae) connected with one another by very fine canals 



Fig. 447. — ^Vertical section of articular cartilage resting on bone, and showing cells 

 and capsules arranged in layers as indicated by numerals (Sappey). 



(Fig. 444). A vertical cross - section exhibits the lamellae of 

 which it is made up and the vascular channels cut across 

 (Fig. 445). 



All this is, however, only the framework of osseous tissue. ^ 

 If a bone from an animal freshly killed, without bleeding, be 

 examined, a very different state of things will be found. The 

 bone is heavier ; its surface is covered with a closely adherent, 

 tough, fibrous structure, the periosteum : and its medullary 

 cavity filled with marrow. If the bone be broken across, its 

 section looks red, and blood flows from the surface. Investiga- 

 tion proves that the covering periosteum is a bed in which 

 blood-vessels and nerves ramify, and from which they enter 



