770 



THE THEORY OF TRANSFORMATIONS 



[CH. 



surprising nor peculiar ; for it is linked with all the considerations 

 of mechanical efficiency and functional modification which we 

 dealt with in our last chapter. The scapula occupies, as it were, 

 a focus in a very- important field of force; and the lines of force 

 converging on it will be very greatly modified by the varying 

 development of the muscles over a large area of the body and of 

 the uses to which they are habitually put. 



Fig. 405. Co-ordinates of chimpanzee's skull, as a projection of 

 the Cartesian co-ordinates of Fig. 404. 



Let us now inscribe in our Cartesian co-ordinates the outline 

 of a human skull (Fig. 404), for the purpose of comparing it with 

 the skulls of some of the higher apes. We know beforehand that 

 the main differences between the human and the simian types 

 depend upon the enlargement or expansion of the brain and 

 braincase in man, and the relative diminution or enfeeblement of 

 his jaws. Together with these changes, the "facial angle" 

 increases from an oblique angle to nearly a right angle in man, 



