XVII] THE COMPARISON OF RELATED FORMS 771 



and the configuration of every constituent bone of the face and 

 skull undergoes an alteration. 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 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 co-ordinate network 

 intersected in the human skull, we find that these corresponding 

 points may be at once linked uj5 by smoothly curved lines of 

 intersection, which form a new system of co-ordinates and con- 

 stitute a simple "projection" of our human skull. The network 



Fig. 406, Skull of chimpanzee. Fig. 407. Skull of baboon. 



represented in Fig. 405 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. 406 demonstrates 

 the correspondence. In Fig. 407 I have shewn the similar de- 

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

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

 an increased intensity or degree of deformation. 



In both dimensions, as we pass from above downwards and 

 from behind forwards, the corresponding areas of the network 

 are seen to increase in a gradual and approximately logarithmic 

 order in the lower as compared with the higher type of skull; 

 and, in short, it becomes at once manifest that the modifications 

 of jaws, braincase, and the regions between are all portions of one 

 continuous and integral process. It is of course easy to draw the 



49—2 



