TRANSFORMATION OF ORGANS OF ANIMALS 4*7 



by all modern monkeys, probably existed at some 

 time in man or his immediate ancestors. 



The terrestrial five-toed foot must have acquired 

 an opposable great toe in the course of adaptation 

 to arboreal life. Without attempting to enumerate 

 all the attendant phenomena of degeneration en- 

 tailed by this modification, we will merely examine 

 those exhibited by the nails of the hind foot. 

 Comparison with the supposed ancestors of the 

 Primates (Insectivores) shows that in the primitive 

 terrestrial foot the nails completely covered the 

 extremities of the terminal phalanges. With the 

 lowest Lemur (Tarsius) the nails of the second and 

 third toes are in the form of claws, while all the 

 others are degenerating; they cover only the 

 anterior face of the terminal phalanges, and are, 

 in fact, flat nails. In all the other Lemurs, only 

 the second toe has a claw, whereas in true monkeys 

 all the nails are flat. Finally, in the Orang the 

 great toe often has no nail at all. 



We then come to limbs adapted to arboreal life, 

 such as those of the Gorilla. With some anthropoids, 

 however, arid especially the Orang, the modification 

 has gone further, and is accompanied by phenomena 

 of degeneration in other parts of the limb. While, 

 in the case of the Gorilla (fig. 21) the great toe 

 has a true articulation between the metatarsal and 

 the first phalanx, and also between the first and 

 second phalanges, with the Orang (fig. 22) the great 

 toe is much reduced so that it has no articulation 



