OSSEOUS' SYSTEM, 187 



Development of the Osseous System. 



Q. At what period is ossification complete ? 



*#. From the eighteenth to the twentieth years. 



Q. What are the states of the bones during growth? 



#. There are the remarkable states of the osseous tex- 

 ture; viz. the mucous, the cartilaginous, and the osseous. 



Q. At what period do you see the mucous state? 



A. It appears in the earliest periods of the development 

 of the embryo, and continues till the vessels commence 

 conveying gelatine. The cartilaginous state succeeds this, 

 and finally the deposition of phosphate of lime takes place. 



Q. What is the first indication of calcareous deposition? 



#. The appearance of red blood in the cartilaginous 

 bed of the bone. This blood enters vessels which formerly 

 conveyed gelatine. There is always in the process of 

 earthy exhalation a red layer which is vascular, between 

 the cartilage and that portion of the bone where calcare- 

 ous deposition has taken place. 



Q. Why do the vessels which once conveyed white 

 fluids, afterwards admit red blood ? 



/2. Such is the fact in the deposition of calcareous mat- 

 ter in ossification, and it proceeds from a change in the 

 relation of the vital forces of the vessels to the fluids, re- 

 ceiving at one time white, at another red fluids. 



Q. At what period does the osseous state commence? 



/?. It appears first in the clavicle, the ribs, &c. about 

 the end of the first month. 



Q. Where do the long bones increase in length? 



/?. Only at the extremities, not in the middle. An ac- 



