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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. Meyers^1,*, 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

View larger version (33K): [in a new window]   Fig. 1. Tongue aiming ability was quantified by having individuals of Phrynomantis bifasciatus aim into five quadrants: (A) left –46° to –105°, (B) left –6° to –45°, (C) 0° to 5° to either side, (D) right 6° to 45°, (E) right 46° to 105°. The quadrant is essentially a bib, with the midline of the head designating 0°. As the head of the animal turns, the quadrant follows this movement so that a line drawn down the midline of the head would always be located at 0°.

View larger version (163K): [in a new window]   Fig. 2. Ventral view of the buccal region of a cleared and stained specimen of Phrynomantis bifasciatus. Left and right sides are nearly identical. Major cranial nerves are labeled on the left side and rami of the nerves that innervate the tongue and hyobranchial musculature are labeled on the right side. Branches of the trigeminal nerve (V) innervate the m. submentalis (1) and the m. intermandibularis (2). Branches of the hypoglossal nerve (XII) innervate the m. genioglossus dorsoventralis, longitudinalis and transversalis (3) and the m. hyoglossus (4). The glossopharyngeal nerve (IX) is dorsal to the hypoglossal nerve and innervates other hyobranchial musculature and the tongue pad. Numbers 1 and 3 are located at the approximate sites of nerve transection for denervation of the m. intermandibularis and m. genioglossus lateralis and dorsoventralis, respectively.

View larger version (21K): [in a new window]   Fig. 3. Ventral view of the superficial throat musculature in two anurans. (A) Undifferentiated m. intermandibularis posterior of a typical frog. (B) Differentiation of the m. intermandibularis posterior into two separate accessory slips in Phrynomantis bifasciatus. mm, mentomeckelian element; sm, m. submentalis; ip, m. intermandibularis posterior; m, mandible; ih, m. interhyoideus; ipa1, m. intermandibularis posterior accessory 1; ipa2, m. intermandibularis posterior accessory 2.

View larger version (45K): [in a new window]   Fig. 4. Sagittal section of the tongue of Phrynomantis bifasciatus. (A) Note that the fibers of the m. genioglossus dorsoventralis are directed longitudinally and then dorso-ventrally. (B) Magnified view of the m. genioglossus dorsoventralis. Single fibers run in both the longitudinal and vertical planes. d, dentary; gh, m. geniohyoideus; ggdv, m. genioglossus dorsoventralis; ggl, genioglossus longitudinalis; h, hyobranchium; hg, m. hyoglossus; im, m. intermandibularis; ggt, m. genioglossus transversalis; m, mucosal layer. Scale bar, 1 mm.

View larger version (113K): [in a new window]   Fig. 5. Examples of tongue aiming in microhylid frogs: (A) Phrynomantis bifasciatus; (B) Dyscophus insularis; (C) Scaphiophryne marmorata; (D) Dermatonotus muelleri; (E) Kaloula pulchra; (F) Callulina sp.; (G) Gastrophryne olivacea; (H) Breviceps adspersus; (I) Microhyla sp.; (J) Probreviceps sp. Note the angle of the tongue in relation to the midline of the head. All pictures were taken with the camera positioned at 45°, except H and J, which were head-on profiles.

View larger version (166K): [in a new window]   Fig. 6. Tongue protraction in Phrynomantis bifasciatus when prey is placed directly in front of the animal. (A) Normal feeding. There is no deviation of the tongue when attempting to capture prey. (B) After right unilateral m. submentalis and m. intermandibularis denervation, the tongue is protracted normally. (C) After right unilateral m. genioglossus (both longitudinalis and dorsoventralis) denervation, the tongue deviates towards the right (inactive) side. Animals are no longer able to capture prey placed directly in front of the head or towards the active side.