xni BONES AND JOINTS 177 



themselves to the periosteum than to the smooth bone 

 itself. The most important function of these mem- 

 branes is to carry nourishment to the bone substance 

 and to keep it in a healthy condition. Blood vessels 

 and lymphatics pass into and through the bone from 



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Marrow 



FlG. 93. The periosteum, partially removed (Johnstone). 



the periosteum and endosteum. If the periosteum is 

 removed from any part of a bone, that portion of the 

 bone soon dies from a lack of nourishment. If a bone 

 is diseased and a piece of it cut out, but this membrane 

 left uninjured, it will form new bone in place of the 

 old in a very short time. At the ends of the bones a 

 layer of cartilage takes the place of the periosteum. 



1. Get a large bone and cut it across and study its structure care- 

 fully. Cut the enlarged end of a bone and notice how its structure 

 compares with that of the shaft. 



2. Remove all the muscle from a portion of the bone, and run 

 the point of a knife along its surface. A thin membrane may be 

 peeled oft". This membrane is the periosteum. 



3. Examine a slide of bone, if possible, under the microscope. 

 Notice how numerous the channels are through which the blood is 

 carried to all parts of the bone. 



128. Cartilage. That which we call the gristle of 

 meat is cartilage. It is really young bone in which 

 there is as yet little mineral matter. Cartilage is firm 



