These are the nose, pharynx or throat (the large cavity behind the nose and mouth), larynx, trachea or windpipe, and bronchi or bronchial tubes. On entering the nose, the air passes through a high narrow passage on each side, the outer wall of which has three projections (the nasal conchae). It then passes down into the pharynx where the food and air passages meet and cross. The larynx lies in front of the lower part of the pharynx and is the organ where the voice is produced (see VOICE AND SPEECH) by aid of the vocal cords. The opening between the cords is called the glottis, and shortly after passing this the air reaches the trachea or windpipe.
The windpipe leads into the chest and divides above the heart into two bronchi, one of which goes to each lung, in which it splits into ﬁner and ﬁner tubes (see LUNGS). The larynx is enclosed in two strong cartilages: the thyroid (of which the most projecting part, the Adam’s apple, is a prominent point on the front of the neck), and the cricoid (which can be felt as a hard ring about an inch below the thyroid). Beneath this, the trachea – which is stiﬀened by rings of cartilage so that it is never closed, no matter what position the body is in – can be traced down until it disappears behind the breastbone.