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

The adaptive radiation of colubroid snakes has involved thedevelopment of numerous prey capture specializations combinedwith conservation of a swallowing mechanism characterized byindependent movements of the right and left toothed bones ofthe skull. Synchronized electromyographic and cinematographicrecordings of swallowing in Nerodia, Elaphe, Heterodon and Agkistrodon,four diverse genera of colubroid snakes, allow a preliminaryevaluation of the relationship between prey capture and swallowing.The results indicate that the movements of the palatopterygoidbar and advance of the mandible as closing of the jaws beginsas well as patterns of muscle activity producing these movementsare similar among the four genera. Conversely, the patternsof activity of external adductors and, to some extent, the depressormandibulae differ among the four genera sampled. Analyses ofbone movements during swallowing suggest that swallowing iseffected primarily by the palatopterygoid bars. The mandiblesand their connecting soft tissues mainly press the prey againstthe palatopterygoid teeth. The mandibular teeth evidently playlittle active role in swallowing. Also, the maxilla, which displaysconsiderable morphological diversity among colubroid snakes,has little independent or direct function in swallowing, itsteeth rarely contacting the prey. The data suggest that theheads of colubroid snakes have evolved two partially separatedstructural-functional units, a medial swallowing unit and alateral prey capture unit.