I 7 6 



HUMAN PHYSIOLOGY 



CHAP. 



be if they were solid. At the ends a long bone is rather 

 spongy, while the shaft is very compact in structure. 



Under the microscope a thin slice of bone presents 

 an interesting appearance. Little canals appear run- 

 ning in all directions, and small lakes 

 can be seen throughout the entire mass 

 even in its most solid parts. Blood and 

 ^ lymph flow through these canals and 

 ^ permeate the bone from the outside to 



Marrow 

 cav/ty 



Hard 



FIG. 92. A cross-section of bone, highly magnified 

 (Kocher). 



its very center. Bones grow, and hence 

 must have food material carried to them 

 and waste matter removed from them. 



Bone is covered with a very thin, 

 tough connective tissue membrane called 

 the periosteum, and the hollow shaft 

 of the long bones is lined with a some- 

 what similar membrane known as the 

 endosteum. These are very important membranes. They 

 fit over the bony surface very smoothly and thus serve 

 to protect the bone. Muscles can more easily attach 



FIG. 91. The right 

 femur cut open 

 (Zuppke). 



