344 POPULAR SCIENCE MONTHLY 



tive mammals were plantigrades, resting the whole surface of the foot 

 upon the ground in running. This posture is not favorable for rapid 

 locomotion, as instanced by the lumbering gait of the bear. It has 

 been retained only by animals which, through burrowing, swimming, 

 climbing or means other than speed are enabled to escape their enemies 

 or obtain their food. But both to beasts of prey and to their quarry 

 increased speed and leaping power would be of great advantage in the 

 struggle for existence. To obtain this advantage they had recourse to 

 the same expedient to which on occasion plantigrade man still resorts 

 — they ran upon their toes. If by variation, the digitigrade position 

 became gradually, or suddenly, the fixed posture of the foot in progres- 

 sion, the structure of the digits would soon be affected. Provided that 

 the feet were used only in locomotion, the shorter digits would not 

 reach the ground. Being useless, they might soon disappear. The 

 reduction of the digits has, therefore, been ascribed simply to the adop- 

 tion of the digitigrade posture. This is, indeed, the chief, but it is 

 not the only factor. It does not explain why the hallux of the dog 

 and cat has atrophied, while the pollex persists ; why the pig and water- 

 deer have four digits, the giraffe and camel only two, though all are 

 digitigrade. 



There are evidently three factors upon which the degree of digital 

 reduction depends: (1) the specialization of the extremity for loco- 

 motion; (2) the degree of perfection to which the digitigrade posture 

 is carried; (3) the character of the ground which the animals traverse. 



The hallux of the dog and cat has been reduced, because the pes is 

 used only for progression and in the digitigrade position. The pollex 

 of these animals has been retained, as the claw is useful to the cats in 

 climbing and in catching their prey — to the dogs and wolves in burrow- 

 ing and in holding their prey. It is interesting to note that the pollex 

 is no longer a functional organ in the manus of the hyena, an animal 

 which feeds chiefly on carrion. 



To the Carnivora, which are beasts of prey, a padded foot and sharp 

 claws are necessary structures. We, therefore, find that the digitigrade 

 posture is not developed to the extreme. These animals run upon the 

 ball of the foot ; whatever may be the character of the country traversed, 

 all four toes are used in progression, and no further reductions have 

 taken place. 



To the herbivorous ungulates claws are useless structures, and in 

 escaping from their foes noise is no drawback. Speed is their chief 

 requirement and this is increased by leaping from the tips of the toes. 

 This method of progression would blunt the claws, which would then 

 be modified to protect the toes. 



If the digitigrade position is not well developed (as is the case 

 with the slow, heavy ungulates like the elephant, tapir and rhinoceros) 

 all the toes, or all but the first, may reach the ground and function in 



