EVOLUTION OF THE PRIMATES AND MAN 467 



forwards. The ordinary superposition of median vertical 

 sections through skulls suffers from the fact that it is then 

 difficult to distinguish between differences of actual size and 

 differences of development. This difficulty vanishes when the 

 sections are superposed on a common centre, and then rotated 

 so that certain standard radius-lines coincide. Other lines 



Fig. 182. — The skeletons of Neanderthal man and of modern man com- 

 pared. (From JBoule.) 



can then be read-off by angular measurement regardless of the 

 actual size of the skull. The centre of gravity is chosen as the 

 common centre since it is the morphological centre of form. 

 It may be called Sollas' centre. The sections are then rotated 

 so that the radius-lines from the centre to the middle of the 

 foramen magnum coincide. The sections are then " set," 

 and reference-lines are made by continuing the radius of 



