The air enters the trachea, or windpipe, through
a relatively narrow slit in the larynx, or voice-
box, known as thfe glottis, or chmk of the glottis,
which is wider when air is being taken in {inspira-
tion) than when it is being expelled {expiration) j
Life depends on this chink being kept open. The
windpipe is composed of a series of cartilaginou^
or gristly rings connected together by softer tis-
sues. These rings are not entire, but are com-
pleted behind by soft tissues including muscle. It
follows that this tube is pliable and extensible — a
very important provision, especially when large
movements of the neck are made, during vigorous
exercise, and also in singing and speaking.
The bronchial tubes are the tree-like branches
of the trachea, and extend to the air-cells them-
selves, which may be considered as built up around
them in some such fashion as a toy balloon on its
wooden stem, but with many infoldings, etc. (Fig.
10). The air-cells are composed of a membrane



48 VOICE PRODUCTION

which may be compared to the walls of the balloon,
but we are of course dealing with living tissue
supplied by countless blood-vessels of the most
minute calibre, in which the blood is brought very
near to the air which passes over them.
