558 ORGANS OF RESPIRATION. 



over their inferior surface, inspiration is effected, as in frogs, 

 by the movements of the os hyoides and the pharynx, and 

 expiration chiefly by the abdominal muscles ; and from the 

 fixed condition of the osseous elements surrounding the 

 trunk, the resistance of the distended capacious lungs is 

 necessary to assist in all discharges from the body. 



From the length and movements of the neck, the trachea is 

 generally elongated in fresh water and marine chelonia, as 

 in birds, and is surrounded, as in them, with complete cartila- 

 ginous rings ; it sometime divides, in the land species, into 

 two bronchial branches nearly as high as the larynx, one of 

 which proceeds along each side of the neck, protected from 

 compression during the retracted state of the head, by entire 

 tracheal rings. The epiglottis is only a membranous fold 

 across the anterior part of the opening of the glottis, but the 

 rudiments of the vocal chords extend further into the larynx, 

 and are more developed in chelonian than in other reptiles. 

 The vibratile cilia, which line the nasal and buccal passages, 

 the pharynx and oesophagus, and the larynx, trachea, and 

 interior of all the pulmonary organs of amphibia and reptiles, 

 are most remarkable for their tenacity of life in the lungs of 

 chelonia, where they have been observed in activity for seve- 

 ral weeks after death, and on portions detached from the 

 body, even when putrefaction had commenced. The two 

 bronchi of chelonia, enter the inner portion of their corres- 

 ponding lungs, and in traversing the whole extent of these 

 organs, they open as in birds, by numerous lateral perfora- 

 tions, into the large saccular cells of the lungs, which are 

 regularly disposed in outer and inner series, as shown by 

 Bojanus in the emys. 



In birds, as in insects, the inspired air is transmitted through 

 almost every part of the body, and the blood sent through 

 the branches of their systemic vessels is freely aerated, as 

 well as that contained in the vessels of the lungs. The 

 pulmonary organs of birds present a form intermediate be- 

 tween those of reptiles, extended through the abdominal 

 cavity, and those of mammalia, confined to the thoracic por- 

 tion of the trunk. The large cells prolonged from the ends 

 of the bronchi, still reach the posterior part of the abdomen, 

 like the lungs of fishes, amphibia, and reptiles ; and as the 

 lungs are not collected into the anterior part of the trunk, 



