26 STUDIES IN LIFE AND SENSE. 



it remarked, with the anterior pair of limbs in lower life and 

 speedily there ensues an adaptation of means to ends, and all in the 

 direction of the economical conversion of the lower to the higher type 

 of being. The head becomes balanced, and not secured, as we have 

 seen, and thus a saving of muscular power is entailed. Adjustments 

 of bones and joints take place, and the muscles of one aspect, say 

 the front, of the body, counterbalance the action of those of the other 

 aspect, the back ; and between the two diverging tendencies the 

 erect position is maintained practically without effort. So, also, in 

 the petty details of the work Nature has not been unmindful of her 

 " saving clause." We see this latter fact illustrated in the disposition 

 of the arrangements of foot and heel. One may legitimately an- 

 nounce that man owes much to his head ; but the truth is he owes a 

 great deal of his mental comfort and high physical economy to his heels. 

 The heel-bone has become especially prominent in man when com- 

 pared with lower forms of quadruped life. It projects far behind the 

 mass of foot and leg, and thus forms a stable fulcrum or support, 

 whereon the body may rest. Here, again, economy of ways and 

 means is illustrated. There is no needless strain or active muscular 

 work involved in the maintenance of the erect posture in man. It is 

 largely a matter of equipoise, wrought out through a scheme of 

 adaptation which takes saving of power and energy as its central idea. 



Physiological research lays bare many other points in human and 

 allied life which bear out the contention and principle that natural 

 economics is a powerful and prevailing reality of life. Muscles are 

 ordered, for example, on the plain principle of single acts and of 

 divided tasks. Thus a man bends his forearm on the upper arm 

 largely by aid of the familiar "biceps." This done, the "biceps" 

 retires from the field of work. The arm is straightened by the action 

 of a different muscle, the " triceps." So, also, with the shutting and 

 opening of the hand. While the " flexors " of the fingers placed on 

 the front palm or surface of the limb close the hand, it is the " ex- 

 tensors " of the opposite aspect of the forearm (whose sinews we see 

 in the back of the hand) which open or extend our digits. There 

 may be multiplication of organs here, it is true ; but, given the 

 original power to produce them, there is a clear economy of vital 

 wear and tear exercised in the avoidance of too onerous tasks being 

 laid upon any one muscle. 



It is something of this principle which we find reflected also in 

 the circulation of the blood. Here we see the heart's left ventricle 

 (or larger cavity of the left side) driving blood, as does a force-pump, 

 out into the great system of arteries, which everywhere throughout 

 the body carry the nutrient stream. No sooner, however, has the 

 blood-stream, impelled by the contraction of the muscular walls of 

 the heart's ventricle, passed into the great main artery (the aorta) 



