DAWSON*, Beth; SNEARY, Michael: Morphology of the Cochlear Duct and Saccule of Amphisbaenians

The morphology of the auditory sensor, the basilar papilla, has been studied in many species of lizards and snakes and is known to be highly variant at the family level among lizards, while showing little diversity among all the families of snakes. The structure and function of the papilla of the third suborder of squamates, the amphisbaenians, is less well known. The subject of this study is the morphology of two regions of the inner ear in five species of the family Amphisbaenidae: the cochlear duct, containing the auditory sensor – the basilar papilla, and the adjacent saccule, containing the saccular macula. Results from scanning electron microscopy show that the basilar papilla is ovoid in shape, relatively small, and includes a low density of randomly placed hair cells. Hair cells display stereovillar bundles with a distinctly bulbed kinocilium about the same height as the adjacent row of stereovilli. The orientation of hair cell bundles is predominantly unidirectional (oriented away from the neural side of the papilla), the same seen in snakes, turtles and crocodilians but different than the complex patterns of bidirectionality observed in lizards. The saccular macula has an unusually large otoconial mass resting on its surface. The size of this mass and the connection between it and the hair cell bundles beneath suggests that amphibaenians possess the ability to detect ground-borne vibrations, a distinct advantage for a fossorial organism. These results are discussed in light of the phylogenetic relationships of squamate reptiles and the potential for electrophysiological research to quantify the nature of the auditory senses in these fascinating reptiles. Supported by NIH (MBRS) Grant GM 08192-19.