Meeting Abstract

50.6  Jan. 6  On the structure and function of the inner chamber of the facial pits of pitvipers (Viperidae: Crotalinae) YOUNG, Bruce A.; FAHEY, Anna; KROCHMAL, Aaron R.*; Washburn University; Washburn University; University of Houston – Downtown krochmala@uhd.edu

Pitvipers (Viperidae: Crotalinae) are named for their paired, thermally-sensitive facial pits located midway between the eye and nostril on either side of the head. Empirical studies of these organs have traditionally focused on their functional utility and neurophysiology, leaving certain anatomical aspects unexamined. The facial pit membrane, a ca. 15 micron thick sensory membrane, is suspended across the pit cavity, dividing the pit into an inner and outer chamber. The inner chamber is connected to the external environment by means of a narrow duct that terminates in a pore located beneath the posterior edge of the lower preocular scale. Lynn (1931) claimed that this pore was surrounded by a sphincter muscle, but provided no anatomical or histological evidence in support of this. We used standard microdissection and histological techniques to survey the anatomy of the inner facial pit chamber and the associated duct and pore in a representative sample of pitvipers. The duct, exit pore, and surrounding sphincter are a consistent feature of this sensory organ in all species examined. Further, the sphincter muscle surrounding the pore is under direct neurological control. The function of the inner chamber and duct remains unclear, but our anatomical evidence is consistent with its utility as a heat disperser as first conjectured by Klauber (1972), or as a means to vent pressure built up in the inner chamber as a result of heating the facial pit membrane. Future studies focusing on the causes and consequences of the contraction of this sphincter muscle are needed to fully address its function.