^ 



ENLARGEMENT OF PARTS FROM USE. 15 



exhibited to a class of students, this large secon toe was 

 mistaken for the hallux (fig. 8). This observation is of 

 interest, the large size of the first toe and the great 

 development of its muscles are owing to the greater use 

 and importance of the hallux in mammals which main- 

 tain an erect, or semi-erect, position when walking along 

 the ground as in man, or climbing trees as in monkeys 

 and phalangers. Humphry, in reference to the large 

 development of this toe, says, " Man literally stands in 

 the animal world on his great toe." 



FIG. 8. Enlargement of the second toe subsequent to 

 amputation of the hallux. 



The same remarks apply to the thumb : in man 

 increased function develops its special muscles, thickens 

 the bone, and toughens the nail. Even among quadru- 

 mana the pollex may be absent (Ateles) ; in such a high 

 form as the chimpanzee the thumb is slender, short, and 

 insignificant. In man we may attribute the dispropor- 

 tion of the hallux and pollex, in comparison with the 

 neighbouring digits, to inheritance through a long line of 

 ancestors of gradual increments of size induced by 



