21t ADAPTATION OF THE HUMAN SKELETON 



pers of Aquitaine, concur in testifying to the intensity of 

 those varied powers, when educed by habit and by skilled 

 practice. The perfection of almost all modifications of 

 active and motive structures seems to be attained in the 

 human frame, but it is a perfection due to especial adapta- 

 tion of the vertebrate type, with a proportional depart- 

 ure from its fundamental pattern. Let us see how this 

 is exemplified in the skeleton of man (Fig. 46), viewing 

 it from the foundation upwards. 



In the typical mammalian foot, the digits decrease from 

 the middle to the two extremes of the series of five toes ; 

 and in the modifications of this type, as we have traced 

 them through the several gradations (pp. 185, 187, Figs. 

 85-39), the innermost, ?", is the first to disappear. In man, 

 it is the seat of excessive development, and receives the 

 name of "hallux," or "great toe;" it retaios, however, its 

 characteristic inferior number of phalanges. The tendons 

 of a powerful muscle, which in the orang and chimpanzee 

 are inserted into the three middle toes, are blended in 

 man into one, and this is inserted into the hallux, upon 

 which the force of the muscle now called "flexor longus 

 pollicis" is exclusively concentrated. 



The arrangement of other muscles, in subordination to 

 the peculiar development of this toe, makes it the chief 

 fulcrum when the weight of the body is raised by the 

 power acting upon the heel, the whole foot of man exem- 

 plifying the lever of the second kind. The strength and 

 backward production of the heel-bone, c, relate to the 

 augmentation of the power. The tarsal and metatarsal 

 bones are coadjusted so as to form arches, both length- 

 wise and across, and receive the superincumbent weight 

 from the tibia on the summit of a bony vault, which has 

 the advantage of a certain elasticity combined with ade- 



