Adult Xenopeltis have bodies that appear slightly flattened, but otherwise similar to pipe snakes. The dorsal half of the body is a dark, purplish brown, while the ventral half is white, light gray, or light yellow. On the head the yellow extends onto the upper labial scales. The young have a distinct light ring around the rear of the head and anterior neck. The head is wedge-shaped and flattened. The tail comprises about a tenth of the total length and has paired subcaudal scales. Scales on the body are large, typically in 15 rows throughout the length of the trunk, head plates are reduced in number and large, and the eye is small. These snakes have a number of unusual anatomical features, including teeth on the premaxilla, mobile attachment of teeth (hinged teeth) on all of the toothed bones, a left lung about half the length of the right lung, no pelvic vestiges, a palate
The common sunbeam snake's (Xenopeltis unicolor) scales appear iridescent as it moves along the forest floor in China. (Photo by Animals Animals ©Joe Mc Donald. Reproduced by permission.)
tightly attached to the snout, but a snout and facial region (maxilla, prefrontals) that can move up and down on the braincase, and an extraordinary mobile toothed process on the dentary bone that extends backward more than half the length of the lower jaw. Their quadrate is short and vertically oriented and is attached dorsally to a supratemporal partially embedded in the bones roofing the ear. Unlike macrostomatan snakes, the anterior tips of the lower jaw in Xenopeltis are tightly bound, as are the maxillae to the premaxilla. The lower jaw also has long, splintlike coronoids and a mobile intramandibular joint.
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