Air Sacs

Air sacs, thin-walled, air-filled outgrowths of the lung walls in birds and some reptiles. Among reptiles, air sacs are developed, mainly in chameleons (also in Geckonidae and Varanidae), where they appear as numerous, variously shaped protrusions of the lung. In birds, air sacs are widely distributed and extend from the ventral side of the lungs; one distinguishes the interclavicular, two pairs of thoracic, one pair of abdominal, and several pairs of less constant air sacs. They not only fill the spaces between internal organs but also penetrate into the bones of birds (into the humerus, sternum, parts of the vertebrae, ribs, pelvic girdle, and sometimes into the limbs, up to the very ends of the phalanges of the fingers).