DEVELOPMENT OF BONE. 



133 



rings remaining without essential change, to a plane in which 

 proliferated cells appear between the calcified trabeculse. This 

 also immediately becomes evident if we return to the exami- 

 nation of a longitudinal section. 



The appearance presented by a longitudinal section is fur- 

 ther rendered very remarkable by the circumstance that the 

 elongated spaces bounded by the above-described calcified 

 trabeculse, suddenly, at a tolerably well-defined limit (g, fig. 12), 

 change their contents from large cartilage cells to a material of 

 a different nature. This consists of granular cells that lie closely 



Fig. 13. 



Fig. 13. Transverse section through foetal cartilage in which ossifica- 

 tion has commenced. 



compressed against the cartilage. These cells are provided 

 with a variable number of longer or shorter processes, which, 

 however, can only be well seen in preparations that have been 

 teased out with needles, or pencilled out with a brush. If we 

 follow up the trabeculse surrounding these masses in the direction 

 of the cartilage, we shall see that the granular cells, accumu- 

 lated where the cartilage commences, form an epithelium-like 

 layer investing the surfaces of the expanded prolongations of 

 the vertical trabeculse, whilst the middle part of the contained 

 mass is occupied by delicate fusiform or stellate cells, amongst 



