ON THE LAWS OF DIGITAL REDUCTION. 501 



The Chrysochloris amongst moles offers an instance where the digital re- 

 duction has taken place in the anterior extremity, where also the mechani- 

 cal strains are most frequent and severe. The same fact is observed in 

 Cydothurus, a little South American arboreal ant-eater, where but two func- 

 tional toes remain upon the fore foot. In the great ant-bear (^Myrmecopha- 

 ga), the third digit of the manus is the strongest, the others evidently un- 

 dergoing reduction, while the former is being constantly augmented by the 

 strains to which it is subjected in obtaining insect prey. 



The sloths of both recent and extinct groups furnish an instance where 

 the number of toes has been reduced from the typical number five to as few 

 as two in one pair of extremities in the living Cholcepiis. The digits also in 

 recent species are of about equal length, which cannot be said of the extinct 

 terrestrial species, where in some cases [Mylodon and Megalonyx) considera- 

 ble inequality existed. The equality in existing species is no doubt due to 

 the equality of tractile strains upon each one of the digits, owing to the 

 peculiar method of climbing and hanging to the limbs of trees by the great 

 hook-like claws. 



The frequent reduction in the number of toes in the foot before it com- 

 mences in the hand is seen in the carniverous groups Felidce (cats) and Ca- 

 nidce (dogs), in odd-toed angulates, in the swift-foot terrestrial Bodentia, £ind 

 universally amongst such animals as perform locomotion entirely by leap- 

 ing with the hind feet, as the kangaroos and jumping mice. Upon this 

 point it may be observed that these creatures all more or less decidedly leap, 

 or else pitch the body through'space in rxmning, mainly by means of the 

 hind limbs. The effect of this unequal distribution of strains has shown 

 itself in the hypertrophy of certain digits And their consequent specializa- 

 tion at the expense of the atrophy of the others. The direction in which 

 growth force is manifested is here determined, as it is determined in all 

 kinds of work or exercise, by the increased development of parts most ex- 

 ercised, and shows that the claims of a certain surgeon,''who is said to have 

 been able to tell the occupation of tradesmen by inspecting the development 

 of the muscles upon the body, are not without foundation. Two cases of 

 this kind have fallen under my own observation, one in the person of a cai'- 

 penter and Another in that of a blacksmith. 



It may be well to note in this place that man, the on] y primate whose 

 feet serve exclusively for purposes of locomotion, belongs to the foregoing 

 class. The outer toes in man are weaker, shorter and less developed than 

 in any of the higher apes, and what may eventually be the fate of these 

 outer toes, if, as many do, he keeps on wearing shoes that a savage would 

 not wear for a single hour, combined with the structure now admirably 

 conditioning a gradual reduction, only our descendants will be able to de- 

 termine a thousand years hence. 



The lines of bones through which strains have been directed are in some 

 way determined by the uses which the feet serve in the life of the animal 

 and its ancestral series. This is supported by the fact that where the strains 



