Page:Popular Science Monthly Volume 40.djvu/703

Rh man. It follows therefore that, as is the case with many vestigial structures and useless habits, we must look back into the remote past to account for its initiation and subsequent confirmation; and whatever views we may hold as to man's origin, we find among the arboreal quadrumana, and among these only, a condition of affairs in which not only could the faculty have originated, but in which the need of it was imperative, since its absence meant certain and speedy death.

It is a well-known fact that the human embryo about three months before birth has a thick covering of soft hair, called "lanugo," which is shed before a separate existence is entered upon. At1:he same stage of development the skeleton is found to conform much more to the simian type than later, for the long bone of the arm, the humerus, is equal to the thigh-bone, and the ulna is quite as long and as important as the tibia. At the time of birth the lower limbs are found to have gained considerably on the upper, but still they are nothing like so much larger as when fully grown. Physiologists have explained this want of development of the lower extremities in the fœtus by attributing it to the peculiarity of the ante-natal circulation, in which the head and arms are supplied with comparatively pure oxygenated blood fresh from the maternal placenta, and the lower part of the trunk and legs get the venous vitiated blood returned through the great veins and transferred via the right ventricle and the ductus arteriosus to the descending aorta. This, it is said, accounts for the more rapid growth and more complete development of the head and arms before birth. To assert the exact contrary would be to contradict several great authorities, and apparently to follow the lead of the pious sage who admired the wisdom and goodness of Providence in causing large rivers to flow by great cities. Nevertheless it is well to remember that just as the Sabbath was made for man, and not man for the Sabbath, so the blood-vessels were made for the body and not the body for the blood-vessels. It appears to me much more true to say that the quick arterial blood is sent to the upper extremities because these parts are for the. time being more important, and their growth and development essential to the welfare of the individual, than that they are coerced into a kind of temporary hypertrophy, nolens volens, through having a better blood-supply arbitrarily sent them than is allotted to their nether fellow-members. That this view is borne out by facts can be shown by taking the example of a young animal whose hind quarters are of essential service to it from birth; and for this end we need go no further than the instance, already quoted, of the young foal. Now, in the ante-natal state the foal has just the same arrangement of blood-distribution as the embryo man; yet he is born with a small light head and well-developed hind quarters, so