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First published online January 27, 2004
Journal of Experimental Biology 207, 827-839 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00819

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A three-dimensional kinematic analysis of tongue flicking in Python molurus

Jurriaan H. de Groot^1,*, Inke van der Sluijs¹, Peter Ch. Snelderwaard¹ and Johan L. van Leeuwen²

¹ Section Evolutionary Morphology, Institute of Biology (IBL), Leiden University, PO Box 9516, 2300 RA Leiden, The Netherlands
² Experimental Zoology Group, Wageningen Institute of Animal Sciences (WIAS), Wageningen University, Marijkeweg 40, 6709 PG, Wageningen, The Netherlands

^* Author for correspondence (e-mail: j.h.de_groot{at}lumc.nl)

Accepted 3 December 2003

The forked snake tongue is a muscular organ without hard skeletal support. A functional interpretation of the variable arrangement of the intrinsic muscles along the tongue requires a quantitative analysis of the motion performance during tongue protrusion and flicking. Therefore, high-speed fluoroscopy and high-speed stereo photogrammetry were used to analyse the three-dimensional shape changes of the tongue in Python molurus bivittatus (Boidae). The posterior protruding part of the tongue elongated up to 130% while the flicking anterior portion elongated maximally 60%. The differences in tongue strains relate to the absence or presence, respectively, of longitudinal muscle fibres in the peripheral tongue. Maximum overall protrusion velocity (4.3 m s^–1) occurred initially when the tongue tip left the mouth. Maximum tongue length of 0.01 body length (20 mm) was reached during the first tongue flick. These observations are discussed within the scope of the biomechanical constraints of hydrostatic tongue protrusion: a negative forward pressure gradient, longitudinal tongue compliance and axial tongue stiffness. The three-dimensional deformation varied along the tongue with a mean curvature of 0.06 mm^–1 and a maximum value of 0.5 mm^–1. At the basis of the anterior forked portion of the tongue tips, extreme curvatures up to 2.0 mm^–1 were observed. These quantitative results support previously proposed inferences about a hydrostatic elongation mechanism and may serve to evaluate future dynamic models of tongue flicking.

Key words: snake, tongue, tongue sheet, muscular hydrostat, flicking, curvature, 3-D kinematics, high-speed fluoroscopy, X-ray

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