A previously unreported throat muscle in Scolecophidia (Reptilia: Serpentes), with comments on other scolecophidian throat muscles

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Abstract
A throat muscle, present in Scolecophidia but absent in other snakes, is reported here for the first time. This muscle passes from the genial region of the lower jaw to the mucosa of the floor of the oral cavity. The precise homology of the muscle is uncertain. In Typhlops at least, it appears to receive hypoglossal innervation, and can thus be assigned to the hypobranchial-spinal muscle group. It may have been derived from a lateral portion of the genioglossus that inserts on the floor of the oral cavity, as is found in diverse lizards, or it may have been derived from the snake geniotrachealis. Present evidence tends to favour the former hypothesis. While the evolutionary origin of the scolecophidian muscle remains unclear a new name is required, it is here termed the geniomucosalis, after the regions of origin and insertion. Some major problems of scolecophidian phylogeny are discussed as a background to remarks on the possible cladistic implications of the presence of the geniomucosalis in Scolecophidia. The conclusion is reached that although the muscle further contributes to the considerable phenetic gap between Scolecophidia and other snakes, while its homology remains uncertain the geniomucosalis is of limited significance in a cladistic analysis. Numerous points of difference are noted between my observations on various scolecophidian throat muscles, and observations reported in the literature.