22 ANATOMY FOR NURSES. [CHAP. III. 



ters and mineral salts from the blood in the Haversian canals 

 can find their way to every part. 



The mineral or earthy substance which is deposited in bone, 

 and which makes it hard, amounts to about two-thirds of the 

 weight of the bone. It consists chiefly of phosphate of lime, 

 with about a fifth part of carbonate of lime, and a small portion 

 of other salts. The soft or animal matter consists chiefly of 

 blood-vessels and connective tissue, and may be resolved by boil- 

 ing almost entirely into gelatine : it constitutes about one-third 

 of the weight of the bone. 



In the reunion of fractured bones new bony tissue is formed 

 between and around the broken ends, connecting them firmly 

 together; and when a portion of bone dies, the dead part be- 

 comes separated from the living bone, and if thrown off or 

 removed, a growth of new bone very generally takes place to 

 a greater or less extent. The periosteum is largely concerned 

 in the nutrition and repair of bone; for if a portion of the 

 periosteum be stripped off, the subjacent bone will be liable to 

 die, while if a large part or the whole of a bone be removed, 

 and the periosteum at the same time left intact, the bone will 

 wholly, or in a great measure, be regenerated. 



In the embryo the foundation of the skeleton is laid in cartilage, or in primi- 

 tive membranous connective tissue, ossification of the bones occurring later. 

 The hardening or ossification of the bones is accomplished by the penetration of 

 blood-vessels and bone-cells, called osteo-blasts, from the periosteum. As they 

 penetrate into the cartilaginous or membranous models, they absorb the car- 

 tilage and connective tissue and deposit the true bone tissue at various points 

 until they form the particular bony structure with which we are familiar. 



