=The Midriff= (pl. III, M) is a muscular and movable partition by which the lungs are separated from the abdomen. It is arched upwards like an inverted basin, but when its muscular fibres contract it flattens and descends, thus increasing the capacity of the chest at the expense of that of the abdomen. =The Function of the Lungs= is, as everybody knows, respiration, which may be considered from a mechanical or a chemical point of view. In this little work we are only concerned with the mechanical part of the subject. If we examine the lungs of a calf, which are very similar to those of a human being, we find that they are soft and elastic to the touch, giving out when pressed a peculiar whizzing sound. We may increase their volume by blowing into them through the windpipe, so as to make them double their original size, and then tie up the windpipe. On re-opening the windpipe the air escapes, and the lungs are gradually reduced to their former bulk. Now, by drawing a deep breath we produce the same result in ourselves as by blowing into the lungs of the calf; by holding the breath we produce the same result as by tying up the windpipe--that is to say, we keep the lungs in a state of expansion; and by releasing the breath we are, as it were, untying the windpipe, leaving the lungs to dwindle down gradually to their former size. There is one very material point, however, in which the analogy ceases. It is this: we keep the air in the inflated calf's lungs by tying up the windpipe, and the corresponding act in ourselves would be to hold our breath by muscular contraction of the outlet in the throat. This is precisely what we do in straining, and in lifting heavy weights, &c.; but it should _never_ be done in breathing for vocal purposes. Here it must, on the contrary, be our endeavour to train, to the highest possible degree, the powerful muscles of the chest and of the abdomen, instead of throwing the labour intended for them upon the comparatively weak and delicate muscles governing the outlet of the windpipe.