OF OSSIFICATION. 255 



the metamorphosis of albumenoid bodies, a conclusion which Orf . Q of the 

 is well illustrated by what we observe in the case of the in- organic and 

 cubating egg. In the adult the source of the bone-earth is earthy matter - 

 twofold : in part it is derived from the food, and in part obtained from 

 the remodeling and changes of the bones themselves. In speaking of 

 the composition of milk, we have already described how, through the ca- 

 sein of that secretion, a supply of phosphate of lime is secured for in- 

 fant life. 



At its first formation, bone consists of a gelatinous material, which grad- 

 ually becomes condensed and cellular, presenting what is termed the carti- 

 laginous state. In this material vascular canals arise, which, The process of 

 concentrating toward one spot, give origin to the point or ossification, 

 centre of ossification. Simultaneously, the structure of the cartilage be- 

 comes modified, its nucleated cells are elongated, nucleoli arising, and 

 smaller cells forming. These reach maturity, and are separated from 

 one another by the material derived from the deliquescence of their pa- 

 rent cells, which has simultaneously been taking place. The progress of 

 these changes may be studied by examining the calcifying cartilage near- 

 er and nearer to the point of ossification, to which, as we approach, we 

 find that the cells become more and more numerous, a general arrange- 

 ment into a columnar form being now apparent. 



The deposit of mineral material commences at the point of ossification, 

 and proceeds between the columnar arrangement of cells, lateral branch- 

 es between the individual cells being successively given off, a bony net- 

 work thus arising which is pervious in every part. In the human em- 

 bryo the cartilaginous stage is completed in the sixth week, and ossifi- 

 cation commences first in the clavicle during the seventh. 



Fig, in, Fig. Ill, perpendicular section of the ossifying 



border of the shaft of the femur of a child a fortnight 

 old : a, cartilage in which the cells, the nearer they 

 are to the ossifying border, are in more extended 

 longitudinal rows; , ossifying border: the dark 

 streaks indicate the progressive ossification of the 

 intercellular substance, the clear ones the cartilage 

 cells, which ossify subsequently; c, compact layer 

 of bone near the ossifying border ; d, the substantia 

 spongiosa formed in the osseous substance by ab- 

 sorption, with cancelli, e 1 e, the contents of which are 

 not shown. (Kolliker.) 



Fig. 112, photograph of ossifying cartilage, the 

 dark portions showing the region of complete ossifi- 



Ossifying cartilage, magni- .mi i j. * . i. .L-I 



fied 10 diameters. cation. The columnar arrangement of the cartilage 

 cells s is very apparent. 



