Smooth muscles in the lungs of some urodeles

Abstract

THE effectiveness of the mouth floor pump in amphibians is greatly increased if the distance between the mandibular articulations is considerable. Owing to this fact there is a tendency among these animals to evolve low and broad skulls. The ratio of the height of the braincase to the distance separating the quadrate bones was about 6 in oldest palæozoic amphibians, it was 15 in Eryops, and in some recent anurans it reaches 25 (ref. 1). The lung ventilation in caudate amphibians is performed by the same mechanism as in anurans2, but is probably less efficient, as owing to the shape of the body the distance between the quadrate bones is smaller and the lungs are more elongated. © 1962 Nature Publishing Group.