Confirmation of the passive exhalation hypothesis for a terrestrial caecilian, Dermophis mexicanus

We used electromyography (EMG) to determine whether the terrestrial caecili an Dermophis mexicanus uses hypaxial muscle to assist in exhalation, During inhalation D. mexicanus generates high body cavity pressures using a bucca l pump. Previous workers have hypothesized that exhalation is passive, occu rring when high pressure air in the lung moves to the lower pressure atmosp here when the glottis is opened, This passive exhalation mechanism contrast s with other amphibians which have been shown to use hypaxial muscle to ass ist in exhalation. In this study, we implanted EMC electrodes on the transv erse abdominis: (TA) muscle of two caecilians to record muscle activity dur ing exhalation, We observed no EMG activity from the TA muscle during exhal ation, confirming that D. mexicanus uses a passive exhalation mechanism.