Respiration takes place by a pair of lungs, which are light spongy tissues enclosed in the thoracic cavity.
The thoracic cavity is bound dorsally by the vertebral column and ventrally by the sternum, laterally by the ribs.
On the lower side of the thoracic cavity is the dome shaped diaphragm.
Each lung is enclosed by a double membranous pleura. Atmospheric air passes through the external nostril and nasal passages into the pharynx.
From the pharynx it passes through the glottis into the wind pipe. The anterior part of the wind pipe is enlarged to form the larynx or voice box with its wall supported by four cartilaginous plates.
Inside the larynx lies the vocal cord and its vibrations result in the production of sound. The larynx leads into trachea or wind pipe.
Tracheal walls are supported by rings of cartilage which help in the free passage of air. The epiglottis prevents the entry of food into the trachea through the glottis.
The trachea divides into two branches called the bronchi one entering into each lung and dividing into further branches called bronchioles which end in alveoli.