BONE 



73 



marrow cavities. This central stratum presents a spongy appearance as 

 compared with the denser periphery; it is therefore said to contain 

 spongy or cancellous bone, while the more superficial lamellae contain 

 compact bone. 



In the long bones a similar condi- 

 tion exists in the epiphyses, which 

 consist of a wall of compact bone 

 within which the marrow cavity is 

 subdivided by bony partitions into 

 numerous compartments. The epi- 

 physis consists, therefore,, of spongy 

 bone. The shaft or diaphysis of the 

 bone, however, contains a single large 

 marrow cavity whose walls, except for 

 a thin layer at either end, consist en- 

 tirely of compact bone. A little 

 spongy structure is present for some 

 distance at either end of the shaft, in 

 that portion which adjoins the mar- 

 row cavity. 



The ends and facets of the bones 

 are covered by a disk of hyaline car- 

 tilage, which forms the articulating 

 surfaces of those bones which enter 

 into the formation of the movable 

 joints. These articular cartilages are 

 peculiar in that they are not covered 

 by a perichondrium, and their deeper 

 cells, which adjoin the bone, are so 

 arranged that their long axes are per- 

 pendicular to the free surface, as is 

 the case in the central portion of free 

 cartilaginous plates. Toward the free 

 surface of the cartilage the long axis 

 of the cell lies more nearly parallel to 

 the surface, as is likewise the case at 

 the surface of cartilaginous plates 



elsewhere. In the long bones of younger individuals a plate of hyaline 

 cartilage is found also at the epiphyseal lines between the epiphysis and 

 the diaphysis. This plate, which extends through the entire axis of the 



FIG. 86. TRANSECTION THROUGH THE 

 COMPACT BONY WALL OF A HUMAN 

 METACARPAL BONE. 



a, outer circumferential lamellae; 6, 

 inner circumferential lamellae; c, 

 Haversian canals; d, interstitial lamel- 

 lae; e, lacunae, with delicate radiating 

 canaliculi. From a thin section of 

 ground bone. X 90. (After Kolli- 

 ker.) 



