504 



NA TURE 



[Sei'Temulk 2 I, ihgc 



Everyone acquainted with the ordinary operations of daily 

 life knows how much labour can be saved by attention to the 

 mere mechanical principles involved in their execution. In 

 carrying a heavy load the great object is to adjust it so that its 

 centre of gravity comes as nearly as possible to the vertical axis 

 of the body, as otherwise force is uselessly expended in the effort 

 to keep the entire moving mass in stable equilibrium — a 

 principle well exemplified by the Italian peasant girl when she 

 poises her basket of oranges on her head. Once upon a time a 

 powerful waterman, accustomed to use buckets double the size 

 of those of his fellow-walermen, had the misfortune to have one 

 of them broken. As he could not, then and there, get another 

 bucket to match the remaining one, and wishing to make the 

 best possible use of ihe appliances at hand, he replaced the 

 broken vessel by one half its size. He then filled both with 

 water and attempted to carry them, as formerly, attached to a 

 yoke, one on each side of him. But to his astonishment this 

 arrangement would not work. The yoke became uneven, and 

 the cfifbit to keep it balanced on his shoulders was so trouble- 

 some that he could not proceed. This emergency led to serious 

 reflection, but, after some experimental irials, he ascertained 

 that, by merely making the arm of the yoke on which the small 

 bucket was suspended double the length of the other, he could 

 carry both buckets without inconvenience. 



But let me take one other illustration. Suppose that two 

 burglars have concocted a plan to rob a richly->tored mansion 

 by getting access to its rooms through 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 '.he 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 ihe 

 ladder was balanced perpendicularly, he himself could then easily 

 control it. Moreover, he made the discovery that by resting 

 its weight on each leg alternately, he could gradually thifi its 

 position from one window to another. Thus there was no in- 

 terruption or limit to the ixtent of their depredations. Ex- 

 perience quickened their jjerceptions, and ultimately they 

 became adepts in iheir 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 represents 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 

 his body. 



The continued maintenance of this unique position necessi- 

 tated great changes in the general structure of the body. The 

 solution of the problem involved the turning of the ordinary 

 quadruped a quarter o( a ciicle in the vertical plane, thus placing 

 the axis of the spine perpendicular, and consequently in line 

 with the direction of the posterior limbs ; and to effect this the 

 osseous walls of the pelvrs underwent certain modifications, so 

 as to bear the additional strain put upon them. Slahilily was 

 giver, to the trunk in its new position by the development of 

 special groups of muscles, who-e powerful and combined actions 

 render to the movements of the hun an body their characteristic 

 freedom and gracefulness. Thelowerlimbs 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 he capable of supporting the entire weight of the bo( y 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 at- 

 tached to the spinous processes of the cervical vertebr.-e {Hga- 

 menltun hucIut), 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 ol lo- 

 comotion, were now themselves carried as liail-like appendages, 

 in order to give them as much freedom and range ot 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, Kurthtr, like the haunch-bones, they underwent certain 

 modifications, so as to afford points of attachment to the 

 muicles 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 extension, 



NO. 1247, VOL. 48] 



flexion, pronation, and supination — in which respects the upper 

 limb of man is differentiated from that of all other vertebrate-. 



But it is in the distal extremities of the limbs that the m<sl 

 remarkable anatomical changes have to be noted. The foot is 

 virtually a tripod, the heel and the ball of the great toe beii.g 

 the terminal ends of an arch, while the four cuter digital columns 

 group themselves together to form the third, or steadying, 

 point. The outer toes thus play but a subordinate part in loco- 

 motion, and, as their prehensile function is no longer ot use, 

 they may be said to be fast approaching to the condition of 

 rudimentary organs. The three osseous prominences whith 

 form this tripod are each covered with a soft elastic pad, whith 

 both facilitates progression and acts as a buffer for deadenii g 

 any possible shock which might arise in the course of running 

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

 perforrired by an enormously developed group of muscles known 

 as the calf of the leg, so characteristic of man. The w alker is 

 thereby enabled to use the heel and the ball of the great toe as 

 successive fukrums from which the forward spring is made, ilie 

 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 boh a pillar for supporting the 

 weight of the body, and a lever lor mechanically impelling it 

 forwards. Hence the amount of energy expended in progression is 

 reduced to a minimum, and when estimated proportionally to 

 the size of Ihe body it is believed to be considerably less than 

 that requisite for the corresponding act in quadrupeds. 



The anatomical changes effected in the extremity of th^ upper 

 limb are equally radical, but of a totally different character and 

 scope. Here we have to contemplate the transfornration of the 

 same homologous parts into an apparatus for perforrrring aseiii-:* 

 of prehensile actions of the most intricate character, but amoni; 

 which neither locomotion nor support of the body forms any 

 part whatever-. This apparatus is the human hand, the m(»l 

 complete and perfect mechanical organ nature has yet product'!. 

 The fingers have become highly developed, and can be oppostd 

 singly or in groups to the thumb, so as to form a hook, a clasp, 

 or a pair of pincers ; and the palm can be made into a cup- 

 shaped hollow, capable of grasping a sphere. Nor is there aiiy 

 limit 10 the direction in which many of these manipulations can 

 be performed without any movement of the rest of the body. 

 For example, a pencil held by the thumb and the two foreingerf, 

 as in the act of writing, can be placed in all the direclionsol 

 space by a mere act ot volition. 



The position of such a perfect piece of mechanism at the 

 extremity of a movable arm attached to the upper part of the 

 trunk, gives to man a superiority in attack and defence o«€r 

 all oiler animals, on the same princi] le as a soldier finds 

 it advan'ageous to fight from higher ground. Moreover, he 

 possesses the power to perform a variety of quick movemeni.s, 

 and to assume attitudes and positions eminently adapted lor 

 the exercise of that manipulative skill with which be 

 counteracts superior brute force of many of his antagonisis. 

 He can readily balance his body on one or both legs, can tum 

 on his heels as it they were pivots, and can prostrate 

 himself comfortably in the prone or supine positions. As 

 the centre of gravity of the whole body is nearly in line 

 with the spinal axis, stable equilibrium is easily maintainedty 

 the lumbar muscles. Altogether we have in his physicil con- 

 stitution a combination of structures and (unctions suff.cieolly 

 unique in its tout ensemble to place man in a categoiy by bini- 

 self. But at the same time we must not forget that all his 

 morphological peculiarities have been brought about without tJie 

 destruction of any of the primary and typical homologies com- 

 mon to all the h:gher vertebrates. 



Turning now to the brain, the undoubted organ of the mind, 

 we find in its intellectual and p-ychical manifestations, a cIms 

 of phenomena which gives to man's life-functions their most 

 remarkable character. However difficult it may be for our 

 limited understanding to comprehend the nature of conscious 

 sensation, we are forced to the conclusion that the act in*an- 

 ably takes place through the instrumentality of a few nerve- 

 cells, whose functional activity requires to be renovated in pre- 

 cisely the same manner as the muscular force expended in wilt- 

 ing. The aogregatioii of such cells into ganglia and nerves, by 

 means of which reflex action, consciousness, and a variety of 

 psychicil ])hent.meiia take place, is found to permeate, in a 

 greater or less degree, ihe whole of the Organic world. In the 

 higher vertebrates the seat of these manifestations is almostex- 

 clusively confined to an enormous collection of brain subslai cc 



