CLAESSENS, L.P.A.M.; Harvard University: Analysis of the Kinematics of Lung Ventilation in Crocodylians

The skeletal and soft tissue kinematics of breathing in Alligator mississippiensis were examined by cineradiography as part of a project investigating the evolution of respiratory mechanisms in the Archosauria. Lung ventilation in A. mississippiensis is diphasic and arrhythmic, and consists of apneic phases of variable duration coupled with episodes of consecutive expirations and inspirations. Inspiration is the rest phase, rather than expiration, and a series of lung ventilations typically starts with an expiration and end with an inspiration. In diving alligators, a partial expiration might be at the close of a series of breaths. The inspiratory tidal volume is retained through closure of the glottis.

Expiration is achieved through elastic recoil of the liver and viscera and dorsal rotation of the pubic bones, aided by contraction of the abdominal wall musculature. Inspiration is achieved by a caudad movement of the liver and viscera through the contraction of the diaphragmaticus muscle, and a ventral rotation of the pubic bones through the contraction of pelvic muscles. Costal aspiration breathing generally occurs in concert with pelvovisceral aspiration. During expiration the ribs rotate caudomedially, coupled with a dorsal rotation of the sternum. During inspiration the ribs rotate craniolaterally, coupled with a ventral rotation of the sternum. During apnea, the ribs are maintained in inspiratory position, partially by the pressurizing effect of the liver and viscera on the lungs. In water, the total lung volume and position of the ribs may vary to a degree as a function of buoyancy requirements. A detailed analysis of skeletal movement was undertaken to identify constraints on respiratory kinematics.