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First published online November 24, 2003
Journal of Experimental Biology 207, 21-31 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00715
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Mechanism of tongue protraction in microhylid frogs

Jay J. Meyers1,*, James C. O'Reilly2, Jenna A. Monroy1 and Kiisa C. Nishikawa1

1 Physiology and Functional Morphology Group, Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011-5640, USA
2 Department of Biology, University of Miami, Coral Gables, FL 33124-0421, USA

* Author for correspondence (e-mail: jjm{at}dana.ucc.nau.edu)

Accepted 23 September 2003

High-speed videography and muscle denervation experiments were used to elucidate the mechanism of tongue protraction in the microhylid frog Phrynomantis bifasciatus. Unlike most frogs, Phrynomantis has the ability to protract the tongue through a lateral arc of over 200° in the frontal plane. Thus, the tongue can be aimed side to side, independently of head and jaw movements. Denervation experiments demonstrate that the m. genioglossus complex controls lateral tongue aiming with a hydrostatic mechanism. After unilateral denervation of the m. genioglossus complex, the tongue can only be protracted towards the denervated (inactive) side and the range through which the tongue can be aimed is reduced by 75%. Histological sections of the tongue reveal a compartment of perpendicularly arranged muscle fibers, the m. genioglossus dorsoventralis. This compartment, in conjunction with the surrounding connective tissue, generates hydrostatic pressure that powers tongue movements in Phrynomantis. A survey of aiming abilities in 17 additional species of microhylid frogs, representing a total of 12 genera and six subfamilies, indicates that hydrostatic tongues are found throughout this family. Among frogs, this mechanism of tongue protraction was previously known only in Hemisus and may represent a synapomorphy of Hemisus and Microhylidae.

Key words: tongue protraction, m. genioglossus dorsoventralis, muscular hydrostat, Microhylidae, frog, Phrynomantis bifasciatus, feeding, prey capture


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