BONE 



8 9 



Meanwhile the cartilage continues to grow, especially in length. 

 This is brought about by successive transverse divisions of the cells of the 

 shaft, so that they become arranged in more or less definite longitudinal 

 rows (Fig. 75). The thin transverse walls of the lacunae in these rows are 



Hyaline carti- 

 lage (cells in 

 groups). 



Hyaline car- 

 tilage (cells 

 enlarged). 



' 



Endochondrial bone 



Periosteum / Perichondrial 

 bone. 



Osteoblasts. Osteoblasts. Blood Osteoclasts. 



vessels. Marrow 



cells. 



FIG. 76. FROM A LONGITUDINAL SECTION OF THE PHALANX OF THE FIRST FINGER OF A HUMAN EMBRYO OF 



THE FOURTH MONTH. X 220. 



dissolved more readily than the thicker longitudinal walls, and the deep- 

 blue ragged spicules of calcined matrix which are thus produced, are there- 

 fore generally elongated. Osteoblasts, derived from the primary marrow, 

 arrange themselves on these spicules, and form bone in the same manner 



