1082 THE THEORY OF TRANSFORMATIONS [ch. 



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 



Fig. 547. Human scapulae (after D wight). A, Caucasian; B, Negro; 

 C, North American Indian (from Kentucky Mountains). 



the muscles over a large area of the body and of the uses to which 

 they are habitually put. 



Let us now inscribe in our Cartesian coordinates the outline of 

 a human skull (Fig. 548), 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 



12 3 4 5 



Fig. 548. Human skull. 



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, and the configuration 

 of every constituent bone of the face and skull undergoes an altera- 



