DEVELOPMENT OF BONE. 



47 



of the shaft in a long, or the mid-point of a flat bone, and here the punctum 

 ossificationis , or centre of ossification, is established. What determines 

 the vascular concentration now alluded to, is a question not easily solved, 

 but that it takes place is certain, and the vascular puncturn is the most 

 easily demonstrable of all the phenomena of ossification. 



During the formation of 

 the punctum ossificationis, 

 changes begin to be appa- 

 rent in the cartilage cells. * 

 Originally they are simple ^ 



Fig. 13.* 



^a <&& <Q**ff f. 



$w*. 



nucleated cells ( s Vgu to 

 zifo-Q of an inch in diame- 

 ter), having a rounded 

 form. As growth pro- 

 ceeds, they become elon- 

 gated in their figure, and 

 it is then perceived that 

 each cell contains two and often three nucleoli, around which smaller cells 

 are in progress of formation. 

 If we examine them nearer 

 to the punctum ossificationis, 

 we find that the young or 

 secondary cells have each 

 attained the size of the pa- 

 rent cell (j-ffVff of an inch), 

 the membrane of the parent , 



cell has disappeared, and 

 the young cells are separated 

 to a short distance by freshly 

 effused intercellular substance. 

 a more remarkable 

 change has ensued, 

 the energy of cellule 

 reproduction has 

 augmented with 

 proximity to the os- 

 sifying point, and 

 each cell in place of 

 producing two, gives 

 birth to four, five, or 

 six young cells, 

 which rapidly cle- 



* Figures illustrative of the development of bone; they are magnified 155 times, 

 and drawn with the camera lucida. A. A portion of cartilage the farthest removed from 

 the seat of ossification, showing simple nucleated cells, having an ordinary size of -g-^^ 

 of an inch, long diameter. B. The same cartilage, nearer the seat of ossification ; each 

 simple cell has produced two, which are a little larger than the cells in figure A. 



f The same cartilage, still nearer the seat of ossification ; each single cell of B has 

 given birth to four, five, or six cells, which form clusters. These clusters become 

 larger towards the right of the figure, and their cells more numerous and larger, 

 of an inch, long diameter. 



t The same cartilage at the seat of ossification ; the clusters of cells are arranged in 

 columns; the intercellular spaces between the columns being ,J,, of an inch ir 



Nearer still to the punctum ossificationis 



Fig. 154 



