31 6 JAMES CRAWFORD WATT. 



Plate 3. 



Fig. 37. Photomicrograph of a small piece of bone from the growing fe- 

 mur of a mouse. The bone cells show as small, oval, opaque bodies in the 

 specimen. No discrete particles can be seen in the matrix. Magnification, 

 X 200. 



Fig. 38. Outline sketch made with camera lucida, of the growing bony end 

 of the diaphysis of the humerus of a six months human foetus. Four zones 

 can be distinguished. A, fully formed bone spicules (shown as solid black, 

 marrow spaces white, bone and marrow cells not indicated) with calcium salts 

 fused. B, osteogenic fibres, impregnated with calcium salts in form of minute 

 granules. C, newly forming osteogenic fibres, not yet impregnated with bone 

 salts, and cartilage showing changes preparatory to bone formation. D, un- 

 altered cartilage. Magnification, X 300. 



