When we compare the length of the foot with the leg, beginning from below upwards, we find a regular proportion and one of practical interest, viz., that from the ground to the middle of the patella usually measures twice the length of the foot.
I have now concluded that portion of my lectures which deals with the proportions of the adult human body, and before passing to the final section, in which I shall give some notes as to the growth of the body and its constituent parts, I think it well to make one remark. I have throughout that portion of my remarks which I am now concluding contrasted Marshall's canon of proportion with the careful figures given by Topinard, and the reader can scarcely have failed to notice that the two correspond in a very remarkable and uniform manner. Now, Marshall's rule was devised for artists ; it was intended to meet their requirements, and, so far as I am aware, though here I speak under correction, it is well fitted to do so. It is satisfactory to find that his conclusions are so well grounded and so corroborated by the scientific figures, so that in using his rule, use is made of one which is scientifically accurate, as well as artistically useful. I have now to turn to the consideration of the method of increase of the human body and of its various parts, a portion of my subject which I trust will not be without usefulness and interest.
It will be noticed that the proportions of the infant when first it makes its appearance in the world are very different from those which it has when it arrives at the period of adult existence, and that between these two epochs the proportions are constantly altering, one part of the body chiefly increasing at one time and a second at another. It will also be noticed that the proportion in two sexes, which, as we have seen, are in many instances different in the adult, for some time remain the same during childhood, and that on arriving at a certain age they commence to take on their adult characters and to differentiate from one another.
The facts stated in this section are chiefly from the works of Roberts and Quetelet; having made which acknowledgment, I need not refer more particularly to the author of any individual statement.
As regards height, at the time of birth there is but little difference between the stature of the male and female infant, the average for the former being 19.34 inches, and for the latter 18.98 inches. Thus, the actual longitudinal proportions almost coincide, whilst the relative ones absolutely do so. Between the fourth and the ninth years the relations remain much the same, but towards the thirteenth year the female gets in front of the male, and is larger and heavier. After this period the growth of the male becomes more rapid; he soon passes the female, and eventually the adult differences between the sexes are established. The difference between the sexes in respect to height are due to several causes. In the first place, as noticed above, the female is a little smaller at birth. In the second place, after the thirteenth or fourteenth year the growth of the female is considerably feebler than that of the male, and finally the growth of the former is concluded about two years before that of the latter.
The last of these causes is the most potent in determining the difference in stature, for the initial difference is abolished, or indeed reversed, at the thirteenth year; but at the period when growth is terminated there is an average advantage in stature of males over females of four inches.
Taking the head, this portion of the body is contained three times in the axis at the time of birth, a proportion which is maintained until the fourth year; at the ninth year the axis is three and a quarter times as long as the head, at the fifteenth three and three-quarters, and at the twenty-fifth four times. In relation to the stature, the head is at birth contained four times in the body-length. But we have already seen that in the adult it is contained seven and a half times, from which facts it follows that the head grows only half as rapidly (nearly) as the remainder of the body. As a matter of fact, it doubles its height between the time of birth and that of adult life. This increase is, however, not evenly distributed over the whole head, since the lower part grows more than the upper. This is shown by the fact that the lower part of the nose, which in the adult divides the face into two equal parts, is in the infant placed much nearer to the chin.
The neck, which is short at birth, apparently becomes shorter during the first few years of life; this apparent decrease in size is due to the accumulation of fat at the chin of the infant.
The torso triples in length and in width. The relations of its antero-posterior diameters in the infant and in the adult are as 1 to 2.36; thus, increase in this direction is not as great as in the other two. Quetelet has shown by the employment of two triangles that the increase in size of the torso, like that of the head, is not the same in all its parts. If we construct a triangle having its base situated at a line drawn between the two nipples and its apex at the suprasternal notch, it will be found that the two sides are less in their respective measurements than the base. After the first year this difference is twenty-one millimetres, and this difference is maintained almost exactly throughout the period of development; thus, the growth of this portion is proportionately even. The proportions between the base in the infant and the adult are as 1 is to 2.81, and those of the sides at the same epochs as 1 to 3.41. The height of the triangle in the infant is to that of the adult as 1 to 3.78, so that, as we have seen that the whole torso triples during growth, the increase of this part is more rapid than that of the whole.