168 BONE AND BONE MAKROW 



growth, and is the last portion of fetal cartilage to be transformed 

 into adult bony tissue. 



All those portions of the bone which are not covered by an 

 articular cartilage are supplied with a membranous coat of fibrous 

 tissue, the periosteum. The outermost layer of this membrane 

 consists of interlacing bundles of dense fibrous tissue, in which 

 are the larger blood vessels, whose branches are distributed to the 

 underlying bone. The inner portion of this layer forms a firm 

 fibro-elastic stratum, which in older individuals is closely attached 

 to the surface of the bone. The periosteum of developing and 

 growing bone, however, contains a third or innermost layer, in 

 which are small blood vessels, fine connective tissue fibrils, and 

 numerous small ostejogenic - cells, the osteoWasts. After growth 

 of the bone has ceased, the deepest layer of the periosteum con- 

 tains few small blood vessels and only occasional osteoblasts ; these 

 cells, however, are present in sufficient numbers to accomplish the 

 regeneration of the bone after destruction of its osseous tissue. 

 The medullary surface of the bone is likewise supplied with an 

 osteogenic membrane of fibrous tissue, similar to the periosteum ; 

 it is known as the periosteum internum, endosteum, or membrana 

 medullaris. 



Compact bone, such as that composing the shafts of the long 

 bones, consists of concentric lamella of calcified fibrous tissue, 

 which constitute the Haversian systems, together with groups of 

 parallel laminae, which are interposed between adjacent Haversian 

 systems and are known as the interstitial or ground lamellce. Many 

 of the interstitial lamellae are the remains of Haversian systems 

 which have been partially absorbed during the development of the 

 bone. In a section through the shaft of a long bone the Haversian 

 systems are found in the middle of the wall, while superficial to 

 them and just within the periosteum are a number of lamellae 

 which may be traced much or all of the way around the circum- 

 ference of the cylindrical shaft, and which are known as the outer 

 circumferential lamellce. On the inner surface of the compact 

 bony wall is a similar group of parallel laminae, which adjoin the 

 marrow cavity, and are known as the inner circumferential lamellce. 

 In their finer structure the circumferential lamellae are exactly 

 similar to the cylindrical bony lamellae of the Haversian systems. 



An Haversian System contains a small central canal which is 

 occupied by connective tissue, marrow cells derived from the mar- 

 row cavity during the process of development, small blood vessels, 



