20 



the fact that in Gibbon the so-called supra orbital ridge is less 

 developed than in Macacus. 



This is the case in a still smaller measure in Orang, as appears 

 from a comparison between fig. 4A and 4B. Although we distinctly 

 observe liere an anterior shifting of the orbita, it is only slight. 

 This is why in Orang no supra-orbital ridges have been developed, 

 but only a general thickening of the frontal bone immediately over 

 the orbitae. 



A comparison of the figures 2, 3, and 4 inter se clearly shows the 

 causal correlation between the origin of supra-orbital ridges and the 

 shifting of the orbitae, for the less this shifting, the less strong the 

 ridges will be. 



This appears even more distinctly from a comparison of Fig. 5A 

 and Fig. 5B. 



Fig. 5. 



Fig. 5 A shows a cast of cranial cavity and orbita of a one-month- 

 old child, and Fig. 5B that of an adult man. It will be seen 



