Water drinking in snakes: Evidence for an esophageal sphincter


  • Vincent L. Bels,

    1. Institut Provincial d'Enseignement Supérieur Agricole et Technique, C.A.R.A.H., B-7800 Ath, Belgium
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  • Dr. Kenneth V. Kardong

    Corresponding author
    1. Department of Zoology, Washington State University, Pullman, Washington 99164-4236
    • Department of Zoology, Washington State University, Pullman, WA 99164-4236
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Drinking fluids by snakes, as in many amniotes, requires elevation of water from the substrate into the mouth, then passage through the pharynx into the esophagus. A model of oral transport of fluids in snakes, the buccal-pump mechanism, predicts that snakes possess a functional sphincter guarding retrograde flow of accumulating fluid from the esophagus, and that intraoral transport proceeds sequentially under active pressure generation by the buccal-pump mechanism. Cineradiographic images and kinematic profiles of fluid transport were analyzed to test these predictions. Our results confirm the following: 1) the presence of a temporary esophageal sphincter, which prevents retrograde passage of fluid from the esophagus back into the mouth. 2) During each rhythmic drinking cycle, positive and negative pressure surges generated by the oropharyngeal cavity first aspirate fluid into the mouth then drive it intraorally, past the esophageal sphincter, and into the esophagus where each pulse of fluid contributes to a growing reservoir of water. 3) The oropharyngeal cavity is functionally divided into anterior and posterior tandem chambers that pump fluid sequentially from one (anterior) to the other (posterior), which then empties into the esophagus. 4) In large snakes, capillarity is not a significant force contributing to intraoral transport of water. These findings support the proposed buccal-pump models of fluid drinking by snakes. © 1995 Wiley-Liss, Inc.