468 PRIMARY FACTORS OF ORGANIC EVOLUJ^ION. 



ologists who are not zoologists are not careful to point 

 out these distinctions. 



If the platycnemic tibia has been produced by mus- 

 cular pressure in man, it has been probably so pro- 

 duced in the apes, where it is a universal character. 

 If the early fusion of the sagittal suture is produced 

 by the vigorous contractions of the temporal muscle 

 as suggested by Brinton, in the black race, due to 

 prognathous jaws, this is probably why it is a universal 

 character of the apes, where the jaws are still more 

 prognathous. What may be the cause of prognathism 

 is not explained by archeologists, but has been dis- 

 cussed in my book on the Origin of the Fittest, and by 

 Dr. C. S. Minot. That the prognathous jaws and 

 platycnemic tibia are not found in the foetus by no 

 means proves that they are not inherited characters. 

 Besides the fact already mentioned, that we are by 

 this only thrown back on an inherited muscular struc- 

 ture, it is further to be remarked that characters which 

 indicate the evanescence or degeneracy of parts, do 

 not usually appear in the foetus, but are disclosed at 

 later stages. The prognathous jaws are disappearing 

 from the higher races, and the process of disappear- 

 ance is in this point accomplished by a retention of 

 the foetal face, which is excessively orthognathous. 

 Prognathism is characteristic of most of the lower 

 Mammalia, and whenever man displays it, if he be, as 

 evolutionists believe, descended from some other mam- 

 mal, he is simply continuing to develop the old char- 

 acter in the old manner. The same reasoning applies 

 to the platycnemic tibia and the tritubercular molar. 



As regards the lemurine character of the trituber- 

 cular molar, the term is a good one, as indicating the 

 nearest of kin to man which present such molars. But 



