two
vertical lines is the same, yet B appears much longer than A.

[Illustration: Fig. 147.--To show False Estimate of Size.

\ /
\ /
/|\ |
/ | \ |
| |
A | B |
| |
\ | / |
\|/ |
/ \
/ \
]

Experiment 186. In indirect vision the appreciation of direction is
still more imperfect. While leaning on a large table, fix a point on the
table, and then try to arrange three small pieces of colored paper in a
straight line. Invariably, the papers, being at a distance from the
fixation-point, and being seen by indirect vision, are arranged, not in
a straight line, but in the arc of a circle with a long radius.

Chapter XII.

The Throat and the Voice.

349. The Throat. The throat is a double highway, as it were,
through which the air we breathe traverses the larynx on its way to the
lungs, and through which the food we swallow reaches the oesophagus
on its passage to the stomach. It is, therefore, a very important region
of the body, being concerned in the great acts of respiration and
digestion.

The throat is enclosed and protected by various muscles and bony
structures, along which run the great blood-vessels that supply the head,
and the great nerve trunks that pass from the brain to the parts below.

We have already described the food passages (Chapter VI.) and the
air passages (Chapter VIII.).

To get a correct idea of the throat we should look into the wide-open
mouth of some friend. Depressing the tongue we can readily see the back
wall of the pharynx, which is common to the two main avenues leading
to the lungs and the stomach. Above, we notice the air passages, which
lead to the posterior cavities of the nose. We have already described the
hard palate, the soft palate, the uvula, and the tonsils (Fig. 46).

On looking directly beyond these organs, we see the beginning of the
downward passage,--the pharynx. If now the tongue be forcibly drawn
forward, a curved ridge may be seen behind it. This is the
epiglottis, which, as we have already learned shuts down, like the
lid of a box, over the top of the larynx (secs. 137 and 203).

The throat is lined with mucous membrane covered with ciliated epithelium,
which secretes a lubricating fluid which keeps the parts moist and
pliable. An excess of this secretion forms a thick, tenacious mass