THE STRUCTURE OF THE ELEMENTARY TISSUES. 



51 



which are not converted into bone remain in the spaces of the cancellous 

 tissue as the red marrow. 



Ossification in Cartilage. Under this heading, taking the femur 

 as a t} T pical example, we may consider the process by which the solid 

 cartilaginous rod which represents it in the f(etus is converted into the 

 hollow cylinder of compact bone with expanded ends of cancellous tissue 





fe " M *" siWaa "" 





FIG. 59. 



FIG. 60. 



FIG. 59. Ossifying cartilage showing loops of blood-vessels. 



FIG. 60. -Longitudinal section of ossifying cartilage from the humerus of a foetal sheep. Cal- 

 cined trabeculae are seen extending between the the columns of cartilage cells, c, cartilage cells. 

 X 140. (Sharpey.) 



which forms the adult femur; bearing in mind the fact that this foetal 

 cartilaginous femur is many times smaller than the medullary cavity 

 even of the shaft of the mature bone, and, therefore, that not a trace -of 

 the original cartilage can be present in the femur of the adult. Its 



