High-speed videography and muscle denervation experiments were used to elucidate the mechanism of tongue protraction in the microhylid frog Phrynomantis

identified several morphologically distinct tongue types (Magimel-Pelonnier, 1924; Regal and Gans, 1976; Gans and Gorniak, 1982a,b; Trueb and Gans, 1983), indicating that several mechanisms of tongue protraction might be found within anurans. Subsequent functional studies identified three basic mechanisms of tongue protraction: mechanical pulling, inertial elongation and hydrostatic elongation. The first two mechanisms are widespread among frogs (Nishikawa, 1997, 1999), but the third, hydrostatic elongation, has been found only in the monogeneric family Hemisotidae (Ritter and Nishikawa, 1995; Nishikawa et al., 1999). Mechanical pulling is the primitive mechanism of tongue protraction in frogs. This mechanism is found in all archaeobatrachians (Nishikawa, 1997; Nishikawa and Cannatella, 1991; Nishikawa and Roth, 1991), as well as in some mesoand neobatrachian frogs (Deban and Nishikawa, 1992; O’Reilly and Nishikawa, 1995; Nishikawa, 2000). Mechanical pulling is characterized by a modestly protrusible tongue (less than 70% of jaw length), which is protracted by contraction of the m. genioglossus. As the m. genioglossus shortens, the tongue bunches at the front of the jaws and is extended beyond the mandibular symphysis. Unless a prey item is extremely close to a mechanical-pulling frog, the modest extent of tongue protraction requires forward body movement (lunging) in concert with tongue protraction in order for the tongue to come in contact with the prey (Deban and Nishikawa, 1992; Valdez and Nishikawa, 1996). Inertial elongation is a derived mechanism of tongue protraction among anurans and has evolved at least seven times independently (Nishikawa, 2000). With respect to sheer numbers of species, it is probably the most prevalent mechanism of tongue protraction among living frogs (Nishikawa, 1997, 2000; Nishikawa and Gans, 1995). Inertial elongation is accomplished by tightly coordinated tongue and jaw movements that flip the tongue over the mandibles and extend it well beyond its resting length (Nishikawa, 1992, 2000; Nishikawa and Gans, 1996). The tongue is protracted very fast and is delivered to the target with minimal body movement, allowing the animal to remain relatively cryptic during feeding bouts (Gray, 1997). However, possibly because the tongue movements are ballistic, the frogs are apparently unable to change the trajectory during protraction and have little or no ability to laterally aim the tongue independent of the head. The third known mechanism of tongue protraction in anurans is hydrostatic elongation. In contrast to the other two 21 The Journal of Experimental Biology 207, 21-31 Published by The Company of Biologists 2004 doi:10.1242/jeb.00715