TRANSACTIONS OF SECTION H. 887 



the ■windows of an upper story. In order to carry out this design they secure a 

 ladder, easily transported by the two together though too heavy for one. So, 

 bearing the ladder between them one at each end, they come to the house. After 

 a considerable amount of exertion they succeed in placing the ladder in an upright 

 position against the wall, and then one of the men mounts its steps and enters the 

 house. The man left outside soon realised that, once the ladder was balanced per- 

 pendicularly, he himself could then easily control it. Moreover, he made the dis- 

 covery that by resting its weight on each leg alternately, he could gradually shift 

 its position from one window to another. Thus there was no interruption or 

 limit to the extent of their depredations. Experience quickened their perceptions, 

 and ultimately they became adepts in their respective departments — the one in the 

 art of moving the ladder, and the other in the science of the nimble-fingered 

 gentry. The division of labour thus practised by these two men accurately repre- 

 sents what the attainment of the erect attitude has accomplished for man by setting 

 free his upper limbs from any further participation in the locomotion of liis body. 



The continued maintenance of this unique position necessitated great changes 

 in the general structure of the body. The solution of the problem involved the 

 turning of the ordinary quadruped a quarter of a circle in the vertical plane, thus 

 placing the axis of tlie spine perpendicular, and consequently in line with the 

 direction of the posterior limbs ; and to efi'ect this the osseous walls of the pelvis 

 underwent certain modifications, so as to bear the additional strain put upon them. 

 Stability was given to the trunk in its new position by the development of special 

 groups of muscles, whose powerful and combined actions render to the movements 

 of the human body their characteristic freedom and gracefulness. The lower limbs 

 were placed as widely apart as possible at their juncture with the pelvis, and the 

 thigh- and leg-bones were lengthened and strengthened so as to be capable of 

 supporting the entire weight of the body and of transporting it with due efficiency 

 when required. The spinal column assumed its well-known curves, and the skull, 

 which formerly had to be supported by a powerful muscle attached to the spinous 

 processes of the cervical vertebrse {ligamentwn nuchce), moved backwards until it 

 became nearly equipoised on the top of the vertebral column. The upper limbs, 

 instead of taking part in their original function of locomotion, were now them- 

 selves carried as flail-like appendages, in order to give them as much freedom and 

 range of action as possible. The shoulder-blades receded to the posterior aspect of 

 the trunk, having their axes at right angles to that of the spine. Further, like the 

 haimch-bones, they underwent certain modifications, so as to aflbrd points of 

 attachment to the muscles required in the complex movements of the arms. In 

 the pendulous position each arm has its axis at right angles to that of the shoulder, 

 but by a common muscular effort the two axes can be readily brought into line. 

 The elbow-joint became capable of performing the movements of complete exten- 

 sion, flexion, pronation, and supination — in which respects the upper limb of man is 

 differentiated from that of all other vertebrates. 



But it is in the distal extremities of the limbs that the most remarkable 

 anatomical changes have to be noted. The foot is virtually a tripod, the heel and 

 the ball of the great toe being the terminal ends of an arch, while the four outer 

 digital columns group themselves together to form the third, or steadying, point. 

 The outer toes thus play but a subordinate part in locomotion, and, as their pre- 

 hensile function is no longer of use, they may be said to be fast approaching to the 

 condition of rudimentary organs. The three osseous prominences which form this 

 tripod are each covered with a soft elastic pad, which both facilitates progression 

 and acts as a buffer for deadening any possible shock which might arise in the 

 course of running or leaping. The chief movement in the act of progression is 

 performed by an enormously developed group of muscles known as the calf of the 

 leg, so characteristic of man. The walker is thereby enabled to use the heel and the 

 ball of the great toe as successive fulcrums from which the forward spring is made, 

 the action being greatly facilitated by that of the trunk muscles in simultaneously 

 bending the body forwards. The human foot is thus admirably adapted to be both 

 a pillar for supporting the weight of the body and a lever for mechanically im- 

 pelling it forwards. Hence the amount of energy expended in progression is 



