Activity of Head Muscles During Feeding by Snakes: A Comparative Study

Abstract

The adaptive radiation of colubroid snakes has involved the development of numerous prey capture specializations combined with conservation of a swallowing mechanism characterized by independent movements of the right and left toothed bones of the skull. Synchronized electromyographic and cinematographic recordings of swallowing in Nerodia, Elaphe, Heterodon and Agkistrodon, four diverse genera of colubroid snakes, allow a preliminary evaluation of the relationship between prey capture and swallowing. The results indicate that the movements of the palatopterygoid bar and advance of the mandible as closing of the jaws begins as well as patterns of muscle activity producing these movements are similar among the four genera. Conversely, the patterns of activity of external adductors and, to some extent, the depressor mandibulae differ among the four genera sampled. Analyses of bone movements during swallowing suggest that swallowing is effected primarily by the palatopterygoid bars. The mandibles and their connecting soft tissues mainly press the prey against the palatopterygoid teeth. The mandibular teeth evidently play little active role in swallowing. Also, the maxilla, which displays considerable morphological diversity among colubroid snakes, has little independent or direct function in swallowing, its teeth rarely contacting the prey. The data suggest that the heads of colubroid snakes have evolved two partially separated structural-functional units, a medial swallowing unit and a lateral prey capture unit.