502 ON THE LAWS OF DIGITAL SEDUCTION. 



to lie overcome arc cquallj^ distributed amongst all the digits there is rarely 

 any specialization of toes. In aquatic, marine, and arboreal animals the 

 distribution of strains is comparatively equal, and I now call to mind but 

 a very fcvi^ exceptions to this rule, which is but slightly affected by even 

 these. One case is the Cyclothurus, where, however, the hind foot and tail 

 are modified into grasping organs, leaving the great pair of claws in front 

 for the purpose of tearing up the bark aud getting into crevices in search- 

 ing for insects. The Dendrolagus, or tree kangaroo, is another instance, but 

 here the descent from the terrestrial kangaroos is too obvious to require 

 discussion. In studjang the fossil kangaroos Professor Owen noticed that 

 the fur-claws were not as rudimentary as in the living species, showing that 

 at one time there was a more uniform distribution of strains than now. 



Among fossorial animals it is usual to find the claws and toes well de- 

 veloped upon the fore limbs ; this is so in the moles, armadillos, recent and 

 fossil, and in the Geo77iyidce, or gophers, where the distribution of strains is 

 very unequal in respect to the fore and hind pairs of limbs. So, too, in the 

 group in which man has been included, where the strains are greatest upon 

 the hind pair, as in animal that run rapidly or are capable of making great 

 leaps, like dogs, cats, rabbits, tapirs, cavies, or guinea pigs. 



It seems to us the most convincing proof of the doctrine of descent to 

 find man an instance of the same kind of specialization determined by the 

 manner of the distribution of strains as is so often found among the lower 

 groups, such as the horses, sloths, jumping mice, and even-toed ungulates. 

 We would not put him in respect to foot-structure among the true planti- 

 grades, for unlike them the elements of the digits are not uniformly of the 

 same strength and calibre. He might be somewhat clumsily called an 

 inequidigitate plantigrade. 



J!^ow as to the osteological side of the question : in man the bones through 

 which the line of greatest mechanical strain passes are the first digit, ento- 

 cuneiform, navicular, calcaneum, and astragalus. In the horse this line 

 passes through the third digit, external cuneiform, navicular, astragalus, and 

 calcaneum in the hind foot ; through the third digit, magnum, scaphoid, and 

 lunar in the fore foot. In the kangaroo, through the fifth, but mainly 

 through the fourth digit, the cuboid, calcaneum, and astragalus in the hind 

 foot. It will be noticed also that in the highest member of the highest group 

 it is the first digit that is specialized ; in the intermediate groups that the 

 intermediate digits are specialized ; that next to the very lowest group it is 

 the fourth digit ; and, fnrther, that there are corresponding chains of 

 specialized bones which receive and distribute the strains.* 



The following summary and conclusions are offered : 



1. That the mechanical force used in locomotion duirng the struggle for 

 existence has determined the digits which are now performing the pedal 

 function in such groups as have undergone digital reduction. 



- It may be as weU to note that birds belong in the catagoiy of types vhich have undergone digital 

 reduction. The ostrich, for obvious reasons, is the extreme. Among reptiles, turtles and dinosaurs may be 

 included, both of which stand near the birds in ihe system. 



