XVII] THE COMPARISON OF RELATED FORMS 1083 



tion. We do not know to begin with, and we are not shewn by the 

 ordinary methods of comparison, how far these various changes 

 form part of one harmonious and congruent transformation, or 

 whether we are to look, for instance, upon the changes undergone 

 by the frontal, the occipital, the maxillary, and the mandibular 



Fig. 549. Coordinates of chimpanzee's skull, as a projection of 

 the Cartesian coordinates of Fig. 548. 



regions as a congeries of separate modifications or independent 

 variants. But as soon as we have marked out a number of points 

 in the gorilla's or chimpanzee's skull, corresponding with those which 

 our coordinate network intersected in the human skull, we find that 

 these corresponding points may be at once linked up by smoothly 

 curved lines of intersection, which form a new system of coordinates 



Fig. 550. Skull of chimpanzee. 



Fig. 551. 



of baboon. 



and constitute a simple "projectipn" of our human skull. The 

 network represented in Fig. 549 constitutes such a projection of 

 the human skull on what we may call, figuratively speaking, the 

 "plane" of the chimpanzee; and the full diagram in Fig. 550 

 demonstrates the correspondence. In Fig. 551 I have shewn the 

 similar deformation in the case of a baboon, and it is obvious that 

 the transformation is of precisely the same order, and differs only 



