66 



THE CONNECTIVE TISSUES 



so formed, and new Haversian systems are formed. The central 

 marrow cavity becomes lined with endosteum which resembles 

 periosteum and forms endosteal lamelhe. 



Growth in length of long bones is brought about by the continued 

 formation of more cartilage at the extremities of the shaft and its 

 progressive replacement by bone. (Fig. 36.) Between birth and 

 maturity ossification centers appear in the terminal cartilage pieces 

 or epiphyses and form spongy bone similar to that formed in the 

 vertebrae. In both of these locations Haversian systems are not 

 formed. Each bony epiphysis is separated for some time from the 

 end of the shaft or diaphysis adjacent to it by a plate of cartilage, 

 but at maturity even these plates change to bone so that one con- 

 tinuous bone is formed and growth in length is at an end. The 

 ends of bones retain a disc of cartilage which acts as a pad in the 

 region of joints. 



In the case of endochondral bone formation in the small lower 

 vertebrates, the process of bone deposition appears to be primarily 

 peripheral, little spongy bone being formed in the course of cartilage 

 resorption of the shaft. 



Epiphyval region 



Epiphysial region 



Shaft 



Spongy bone 



Marroir cavity 

 Hard bone 



Fig. 37. — Diagram of a long bone. 



Microanatomy of Long Bones. (Fig. 37.)— Let us take a long bone 

 such as the femur and di\ide a consideration of it into the following 

 parts periosteum, epiphyses, diaphysis, and the marrow. 



Periosteum covers the bone except at the end-surfaces exposed 

 to contact with adjacent bones at the joints where ])erichondrium 

 and a pad of cartilage occur. Periosteum is a dense, fibrous con- 

 nective tissue externally but grades into material of looser texture 

 toward the b(me. It su])ports arteries, veins, lymphatics, and 

 nerves, which are carried into the Haversian canals of the bone by 

 Volkmann's canals. The bundles of collagenous fibers, Sharpey's 



