Studies of the structures that limit gape size in snakes contribute to the understanding of the function and evolution of the ophidian feeding apparatus. Although recent papers have investigated which morphological characteristics are important to gape in macrostomatans, such studies have yet to determine the contributors to gape size in nonmacrostomatans. I directly measured gape circumference by pushing a cone through the buccal cavity of 10 deceased Red-Tailed Pipe Snakes (Cylindrophis ruffus). For each individual, I measured snout–vent length (SVL), several external head dimensions, and the distance between the mandibles while distended on the cone. The soft tissue was removed from the skull to collect osteological measurements. External and osteological measurements were separately modeled with the use of the Akaike Information Criterion to determine which morphometrics were the best predictors of gape circumference. Like other snakes, gape circumference was negatively allometric with both SVL and cranium length. With the use of line equations from similar studies, C. ruffus exhibited a relatively smaller gape circumference than Crotalus atrox and Nerodia fasciata, but similar to Farancia abacura. Of the external measurements, cranium length and head width were the strongest predictors of gape circumference for Cylindrophis. No single osteological dimension was most important among the tested models, as five metrics ranked equally as the strongest predictors of gape circumference. The relatively small gape and stout skull of C. ruffus are likely adaptations for specialization on narrow, elongate prey and a fossorial lifestyle.
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Vol. 52 • No. 4