hollowed out at the bottom. The left shows two and the right three
distinct flaps or lobes. They are only connected by means of the
windpipe (pl. II, W) and its branches.

=The Chest= (pl. III) is an air-tight chamber, which is narrower above
than below. It is formed by the spine at the back, twelve ribs (pl. III,
1 to 11, the twelfth not visible on the drawing), with their inner and
outer muscles on either side, the breast-bone (pl. III, B B) in front,
the root of the neck at the top, and the midriff or diaphragm (pl. I, M)
at the bottom.

=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,
in