A large sinus known as the infraorbital sinus, surrounds the eye and extends into the upper and lower beak. The infraorbital sinus also communicates with the cervicocephalic air sac. This air sac is not a pulmonary air sac and extends along the neck and back of the skull. The nasal cavity filters inhaled airborne particles by means of mucus and small hair-like cilia. These particles enter the nares and are directed by the cilia through the choana and are then swallowed.
Inhaled air is warmed and moistened by the nasal cavity.
The larynx is at the entrance of the trachea. The opening of the larynx is the glottis. Birds differ from mammals in that the larynx does not have vocal chords and therefore is not involved in voice production. The trachea is formed by a series of ring-shaped cartilages, which are completely closed in birds. In mammals the tracheal ring is not completely formed of cartilage, but contains a membranous component.