STUDIES ON VENTILATION OF CAIMAN-CROCODILUS (CROCODILIA-REPTILIA)

The ventilatory mechanics of freely moving C. crocodilus were studied by cinefluorescopy and electromyography. The buccal oscillations served only to flush the internal nares in olfaction. Ventilations were coincident with abdominal oscillations. The larynx ordinarily lies adpressed to the internal nares so that the posterior buccal chamber is excluded from the path of air flow during ventilation and does not contribute to respiratory dead space. The pulmonary pressures may be variably polyphasic and the tracheal flows diphasic. Exhalation involved an anterior shift of the liver by action of the transverse abdominal muscles, while inhalation proceeded due to contraction of the diaphragmatic muscle pulling the liver caudad. The various costal muscles facilitated air flow by shifting the position of the ribs. They also played a role in fixation of the flexible rib cage so that it resisted the aspirating and compressing actions of the hepatic piston. The pattern of muscular activity shifted as the trunk was immersed; expiration became passive and inspiration required increased muscular effort. The ribs, instead of changing position with each breath were comparatively fixed by the costal muscles, while changes in the volume of the pleural cavity were caused almost exclusively by movements of the hepatic piston.