466 The American Naturalist. [June, 



other races, such as the divided malar or os Japonicum. The 

 human premaxillary, a discovery with which Goethe's name 

 will always be associated, is sometimes partially, more rarely 

 wholly, isolated ; it is late to unite with the maxillary in the 

 Australians, and has been reported entirely separate in a New 

 Caledonian child (Deslongchamps) and in two Greenlanders 

 (Carus). The orbito-maxillary frontal suture, cited by Turner 

 as a reversion to the pithecoid condition, is believed by Thom- 

 son, 1 after the examination of one thousand and thirty-seven 

 skulls, to be merely an accidental variation, without any 

 deeper significance. The development of the temporal bone 

 from two centers, observed by Meckel, Gruber and many 

 others, is considered by Albrecht a reversion to the separate 

 quadrate of the sauro-mammalia. This I think is in the 

 highest degree improbable (see " Limits of Reversion "). The 

 open cranial and ' closed facial sutures are apparently asso- 

 ciated with our increasing brain action and decreasing jaw 

 action; in one case the growth is prolonged and the sutures 

 are left open, in the other the growth is arrested and the 

 sutures are closed. 



Is the lower jaw developing or degenerating ? This ques- 

 tion has recently been the subject of a spirited controversy 

 between Mr. W. Piatt Ball, 2 representing the Weismann school, 

 and Mr. F. Howard Collins, 3 supporting Herbert Spencer's 

 view that a diminishing jaw is one of the features of our 

 evolution which can only be explained by disuse. Mr. Col- 

 lins finds that, relatively to the skull, the mass of the recent 

 English jaw is one-ninth less than that of the ancient British, 

 and roughly speaking, half that of the Australian. He 

 appears to establish the view that the jaw is diminishing. 



Closely connected with this is the evolution of the teeth; 

 how are they tending? This we will consider below. 



Variations of the Teeth.— Flower 4 has shown, as regards the 

 length of our molar series, that we, together with the ancient 



irnal of the Anthropological Institute, ] 



