68 ARBOREAL MAN 



arena in which anatomists, philosophers, and even divines 

 have met and done battle. Man has a well-developed 

 thumb, which is opposable to the remaining fingers. He 

 has a big toe, which is w^ell developed, but which is not 

 opposable to his other toes. The human thumb has 

 received excessive praise from philosophers, the big toe 

 has also come in for its share, but upon the question of the 

 homology of the hallux and pollex there is the widest 

 difference of opinion. Arguments upon the question have 

 been carried to extremes. " I have heard a distinguished 

 naturalist say to a class that he would stake anything, 

 short of his eternal salvation, that the thumb corresponds 

 to the little toe, and the little finger to the great toe, and 

 that he should think his life well spent in establishing the 

 doctrine" (Dwight). 



We need not be led aside into any such controversies, 

 for it does not matter to us if the thumb finds its strict 

 serial homologue in the little toe or in the big toe; it is 

 quite certain that in the latter it finds its exact functional 

 equivalent. By way of homology we will be quite satis- 

 fied with the simple fact that, in the mammalian position 

 of the limbs, it is the digit ivhich is situated nearest the 

 middle line of the body that is specialized as the opposing 

 digit. This power to oppose one digit to the remaining 

 members of the series is no part of the heritage of the 

 primitive third segment of the limb ; it is a new develop- 

 ment called forth by the increasing perfection and the 

 increasing needs of the power to grasp. The mere ana- 

 tomical arrangement by which opposition may be pro- 

 duced among the digits is no necessary part of the char- 

 acteristics of the Primates, nor is it alone within their 

 phylum that it is displayed. Some of the very thoroughly 

 arboreal Marsupials have perfected this arrangement, and 

 most of the Phalangers possess an opposable big toe. 

 Even developments such as are seen in the Chameleon, 

 among the Reptiles, and in the Parrots, among Birds, are 

 hinted at in the hand of the Koala (Phascolarctus), in 



