378 PRIMARY FACTORS OF ORGANIC EVOLUTION 



in reaching this result he has applied geometrical meth- 

 ods. "First, the volume of the bones was got at. 

 Next the area of the bearing surfaces and their inclina- 

 tion to the digits were measured. Then giving to the 

 thrust of each metacarpal a value proportional to its 

 volume, the distribution of that thrust can by resolu- 

 tion and composition of forces, be traced through the 

 foot, and the pressure on each surface and bone ap- 

 proximately obtained." Further than this the author 

 does not explain how he reached the result that the 

 trapezoid is too small. It is quite essential that this 

 demonstration should be given if we are expected to 

 accept his conclusion. An essential part of the prob- 

 lem is, however, unnoticed by Mr. Gary ; and that is 

 the condition of the trapezoid in the reptilian ances- 

 tors of the Mammalia. The phylogeny of an element 

 must be known, since it furnishes the " physical basis " 



i of the problem. The fact is that the trapezium, trape- 

 zoides, and the magnum owe their small size to their 



t being the only carpal elements which have not been 

 produced by the fusion of two or more primitive ele- 

 ments of the batrachian and reptilian carpus. The 

 trapezoides moreover occupies a place in a longitudinal 

 series of three elements in the primitive carpus, while 

 the trapezium forms one of a series of only two ele- 

 ments. For similar reasons the cuneiforms are the 

 smallest elements of the tarsus. 



Mr. Gary then proceeds to criticize the explana- 

 tions offered by Professor Osborn and myself, in ac- 

 counting for the origin of certain structures. He finds 

 our explanations to be self-contradictory, and that we 

 also contradict each other. Osborn has supposed that 

 the conules of the molars are produced by friction of 

 the molars of opposite series on each other. I have 



