794 THE POPULAR SCIENCE MONTHLY. 



fore-limbs shall become useful only as grasping, the hind-limbs only 

 as supporting organs. Necessarily, then, the pelvic joint must gradu- 

 ally change its direction from a right, angle to a straight line. The 

 complete result, in fact, is only attained when the hind-limbs and the 

 body form a vertical line, the function of support being performed 

 entirely by these limbs, while the fore-limbs are freed for other func- 

 tions, and so changed as to be specially adapted for grasping. 



This desidei'atum is attained in man, and in man only of all the 

 animal kingdom. 



In the human form, then, we find all the advantages possessed by 

 the mammalia as a class, together with certain important features of 

 development not possessed by any other mammalian animal. Perhaps 

 the most important of these is the fact that in man gravitation is over- 

 come with a less expenditure of muscular force than in any other land- 

 animal. The whole weight of the body stands vertically above the 

 organs of support. The muscles which in other animals act as ropes 

 and levers of support are only called upon in man to preserve his ver- 

 tical position. Evidently much less force is needed to jjreserve verti- 

 cal equilibrium than to support horizontal weights. 



The head, also, which needs muscular support in quadrupeds, in 

 man presses directly downward upon the common center of gravity. 

 And significantly the comj^lete development of the brain tends to per- 

 fect this vertical position, as it yields a rounded and vertically poised 

 Lead. The head in man has but one set of duties to perform, sensory 

 and masticating labors. The hands bring food to it, instead of its hav- 

 ing to seek food ; therefore it has no need of the horizontal position 

 and movements found in quadrupeds. Finally, that there shall be no 

 weight needing muscular support, the fore-limbs hang vertically down- 

 ward, being sustained by bones and tendons instead of muscles. 



Support on the hind-limbs releases the fore-limbs to act as the defen- 

 sive and offensive organs. For their most complete adaptation to this 

 function the position of the shoulder-joint (like that of the pelvic joint) 

 is changed, and the arms become lateral instead of ventral limbs. Fi- 

 nally, the teeth are released from duty as weapons, and are confined to 

 their proper duty as masticating organs. 



Thus only in man does the organic division of labor become com- 

 plete, every function having a separate organ adapted to it alone. And 

 the stores of force are husbanded to a degree not found in any other 

 land-animal, the weight of the body being supported by bones instead 

 of muscles, by adjusting instead of lifting energies. 



And in regard to reproduction man surpasses all other animals, ex- 

 cept the highest apes, in division of labor and localization of function. 

 The young of the human race thus commence life with the best possi- 

 ble preparation, their vital activity being husbanded so that they enter 

 upon their individual life-work at perhaps a higher starting-point than 

 any other animal. 



