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Tongue projection mechanisms. (A) Mechanical pulling, as seen in the tailed frog Ascaphus truei (Nishikawa and Cannatella, 1991). As the genioglossus muscle contracts, the tongue rotates forward. (B) Inertial elongation, as seen in the northern leopard frog, Rana pipiens. Rapid jaw opening and contraction of the genioglossus muscle causes the tongue to rotate forward and elongate. (C) Ballistic projection, as seen in the plethodontid salamander. Muscles organized in a spiral array contract over a thin horseshoe-shaped cartilage to propel the tongue at high speeds. (D) Hydrostatic elongation, as seen in humans. Longitudinal and radial muscle fibers contract to extend the tongue.

Tongue projection mechanisms. (A) Mechanical pulling, as seen in the tailed frog Ascaphus truei (Nishikawa and Cannatella, 1991). As the genioglossus muscle contracts, the tongue rotates forward. (B) Inertial elongation, as seen in the northern leopard frog, Rana pipiens. Rapid jaw opening and contraction of the genioglossus muscle causes the tongue to rotate forward and elongate. (C) Ballistic projection, as seen in the plethodontid salamander. Muscles organized in a spiral array contract over a thin horseshoe-shaped cartilage to propel the tongue at high speeds. (D) Hydrostatic elongation, as seen in humans. Longitudinal and radial muscle fibers contract to extend the tongue.

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Frogs, chameleons and anteaters are striking examples of animals that can grab food using only their tongue. How does the soft and wet surface of a tongue grip onto objects before they are ingested? Here, we review the diversity of tongue projection methods, tongue roughnesses and tongue coatings, our goal being to highlight conditions for effectiv...

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Context 1
... pulling ( Fig. 2A) is employed by amphibians such as frogs and toads. Such animals have a unique anatomy: in most mammals, the tongue is attached to the throat, but in frogs and toads, it is attached to the front of the lower jaw. Frogs and toads use this attachment point to propel the tongue like a mousetrap. The tongue rotates out of the mouth owing to ...
Context 2
... elongation (Fig. 2B) is also used by frogs and toads. It is similar to mechanical pulling in that the genioglossus muscle contracts and causes the tongue to swing outward. In addition, the frog rapidly drops its jaw, giving the tongue an additional boost of speed, reaching velocities of 4 m s −1 ( Nishikawa and Gans, 1996). Jaw-dropping rates in inertial ...
Context 3
... (de Groot and van Leeuwen, 2004;Deban et al., 2007;Deban et al., 1997). The plethodontid 'lungless' salamander tongue uses two spiral arrays of protractor muscles to compress the needle-like arms of a horseshoe-shaped cartilage skeleton. The skeleton folds medially as it and the surrounding soft, sticky tissue are projected out of the mouth (Fig. 2C). Chameleons extend their tongues using an energy storage-and-release mechanism. Cylindrical connective tissue sheaths are longitudinally loaded around a central cartilaginous bone; upon release, the loaded sheaths slide over the Glossary Elastomer A rubbery polymer capable of large strains before permanent deformation. Filiform ...
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... vertebrates have a tongue that possesses both longitudinal and radial muscle fibers, allowing for a high degree of motion control (Fig. 2D) (Kier, 2012). When the tongue is extended, this motion is called hydrostatic elongation. Tongues of this type share properties with octopus arms and elephant trunks, and are collectively called muscular hydrostats. These muscles elongate by taking advantage of their incompressibility, and transmit force through internal pressure. ...
Context 5
... pulling ( Fig. 2A) is employed by amphibians such as frogs and toads. Such animals have a unique anatomy: in most mammals, the tongue is attached to the throat, but in frogs and toads, it is attached to the front of the lower jaw. Frogs and toads use this attachment point to propel the tongue like a mousetrap. The tongue rotates out of the mouth owing to ...
Context 6
... elongation (Fig. 2B) is also used by frogs and toads. It is similar to mechanical pulling in that the genioglossus muscle contracts and causes the tongue to swing outward. In addition, the frog rapidly drops its jaw, giving the tongue an additional boost of speed, reaching velocities of 4 m s −1 ( Nishikawa and Gans, 1996). Jaw-dropping rates in inertial ...
Context 7
... (de Groot and van Leeuwen, 2004;Deban et al., 2007;Deban et al., 1997). The plethodontid 'lungless' salamander tongue uses two spiral arrays of protractor muscles to compress the needle-like arms of a horseshoe-shaped cartilage skeleton. The skeleton folds medially as it and the surrounding soft, sticky tissue are projected out of the mouth (Fig. 2C). Chameleons extend their tongues using an energy storage-and-release mechanism. Cylindrical connective tissue sheaths are longitudinally loaded around a central cartilaginous bone; upon release, the loaded sheaths slide over the Glossary Elastomer A rubbery polymer capable of large strains before permanent deformation. Filiform ...
Context 8
... vertebrates have a tongue that possesses both longitudinal and radial muscle fibers, allowing for a high degree of motion control (Fig. 2D) (Kier, 2012). When the tongue is extended, this motion is called hydrostatic elongation. Tongues of this type share properties with octopus arms and elephant trunks, and are collectively called muscular hydrostats. These muscles elongate by taking advantage of their incompressibility, and transmit force through internal pressure. ...

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... When a significant number of cells has moved from the monolayer to the second layer, a crisscross multilayering of the nematic cell sheets takes place at the topological defect (Sarkar et al. 2023). Such crisscross multilayering is key to many functional tissues, ranging from the heart (Conrad et al. 1997) to the intestine (Huycke et al. 2019) and the tongue (Noel and Hu 2018), and nematic ordering could potentially play a role in their morphogenesis. Beyond multilayering, a key open question is whether topological defects could similarly emerge in 3D cellular tissues, and if they might play a role in biological processes such as invasion or metastasis. ...
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... Whereas tongue projection mechanisms have been extensively studied, the adhesive mechanism of the tongue has received less attention. Recently, several studies have reported on the adhesive properties given by the interaction of tongue surface microstructure and the secreted mucus (Kleinteich and Gorb, 2014, 2015, 2016Noel et al., 2017;Noel and Hu, 2018). The dorsal surface of the tongue in anurans is characterized by fungiform and filiform papillae, which are covered with mucus secreted by specific cells (Iwasaki, 2002;Nalavade and Varute, 1971;Waller, 1849;Zylberberg, 1977). ...
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The evolution of the tongue in tetrapods is associated with feeding in the terrestrial environment. This study analyzes the tongue morphology of two closely related frog species, Telmatobius oxycephalus and T. rubigo, which exhibit contrasting feeding mechanisms. Telmatobius oxycephalus, a semi-aquatic species, relies on its tongue to capture terrestrial prey whereas T. rubigo, a secondarily aquatic species, uses suction feeding not involving the tongue. Through anatomical, histological and scanning electron microscopy analyses, we revealed remarkable differences in tongue morphology between these species. Telmatobius oxycephalus exhibits a well-developed tongue whose dorsal epithelium has numerous and slender filiform papillae. The epithelial cells of the papillae are protruded and have a complex array of microridges. In contrast, T. rubigo possesses a reduced tongue with flat and less numerous filiform papillae. The epithelial cells are completely flat and lack microridges. These findings highlight the remarkable adaptability of lingual morphology in Telmatobius to respond to the contrasting ecological niches and prey capture mechanisms. This study sheds light on the relationship between tongue shape and the different functional demands, contributing to our understanding of the evolution of prey capture mechanisms in amphibians.
... This mode is used by reptilian species to process, transport and swallow any types of solid food with various textures in both water and air. When the tongue is used for food/prey prehension and therefore used as a gripper [86], the tongue must lose its contact with the food just after the capture cycle to be able to move it under the food item and then continue movements under the food to ensure its role in backwards food displacement within the buccal cavity, regardless of the division of the SO (slow opening) phase into SOI (slow opening I) and SOII (slow opening II). Mouth closing plays a major role in the spatial and temporal characteristics of the transport cycles. ...
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Reptilia exploit a large diversity of food resources from plant materials to living mobile prey. They are among the first tetrapods that needed to drink to maintain their water homeostasis. Here were compare the feeding and drinking mechanisms in Reptilia through an empirical approach based on the available data to open perspectives in our understanding of the evolution of the various mechanisms determined in these Tetrapoda for exploiting solid and liquid food resources. This article is part of the theme issue ‘Food processing and nutritional assimilation in animals’.
... The origins of novel hyolingual muscles and skeletal elements in amphibians (Fabrezii & Lobo, 2009) are hypothesized to be key innovations that led to complexly structured and highly mobile tongues found in most tetrapods today. Conversion of aquatic suction feeding to tonguebased prey prehension (Liem, 1990;Noel & Hu, 2018) and ingestion in some fishes (Heiss et al., 2018;Michael et al., 2015) likely also prompted lingual evolution. At the same time, the tetrapod tongue's exceptional mobility and importance in feeding presumably led to its simultaneous use in numerous non-feeding roles, as outlined in Section 3. ...
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... Research on bio-adhesives has mainly focussed on marine sources, bioadhesives produced by terrestrial animals are relatively rare [3][4][5]. Several reptilian species have developed a sticky mucus on highly extensible projectile elastic tongues which have wet-adhesive properties which aid in the capture of food species [6,7]. Moreover the properties of the mucous salivary secretions which coat the tongue have bimodal properties and can be varied from a low adhesive lubricative form to one which has adhesive properties which firmly attach prey species to ensure efficient capture [8][9][10][11][12][13]. ...
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... How does the elephant trunk strain compare to other muscular hydrostats? We compiled the maximum observed strain for the hydrostat appendages of 13 species, including chameleon and mammal tongues, octopus arms, and elephant trunks (20)(21)(22)(23)(24)(25). decreases with increasing body size, a trend that is even supported across sexes in elephants. ...
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... E Xtending and bending are effective ways to improve the workspace of end-effectors in both natural and artificial systems. For example, frogs, chameleons, and anteaters are animals that are well-known for their extendable and bendable tongues that they use to retrieve food from a distance [1]. A robotic manipulator with these capabilities would be advantageous. ...
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Woodpeckers have flexible and extendable tongues that they use to reach their prey through tiny openings in trees and insect burrows. This unique capability of their tongue represents a promising design for a tool for picking up and handling objects in unstructured environments. Although continuum robots can produce dexterous movements because of their few shape constraints, the lack of structural stiffness has restricted their deployment in real-world environments. Inspired by the characteristics of woodpeckers, we designed a robot manipulator that can substantially extend its length and bend its shape in 2D space. This behavior is enabled by a backbone consisting of a chain of rigid joints and two flexible rack gears. The joints increase the payload by structurally supporting the robot. The proposed structure is 4.7 times stronger in vertical bending and 6.2 times stronger in torsion than without rigid links. Feeding the rack gears at the same and different speeds allows the robot to elongate and bend, respectively. We developed a geometric model based on a constant curvature model for motion planning. Experiments show that the robot can follow an arbitrary trajectory at an arbitrary tip angle. Lastly, we showcase various demonstrations, including deployment and storage for the backbone, follow-the-leader (FTL) motion, and whole-arm grasping in the horizontal plane.
... Indeed, the angle between successive layers varies from uncorrelated (cornea cells), to 0° (parallel alignment, skin cells) or 90° (perpendicular or "crisscross" alignment, heart cells) (18,19). Of notice, when contracted/relaxed independently, stacked perpendicular muscle layers allow complex functions and exploration of the third dimension as exemplified by hydrostatic skeletons that actuate the hydra (20,21) or the intestines (22), as well as by muscular hydrostats such as animal tongues (23). As a matter of fact, such principles are used in biomimetic designs of "soft robots" (23). ...
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Exoskeletons, such as scales on fishes and snakes were a critical evolutionary adaptation. Honed by millions of years of evolutionary pressures, they are inherently lightweight and yet multifunctional, aiding in protection, locomotion and optical camouflaging. This makes them an attractive candidate for biomimicry to produce high performance multifunctional materials with applications to soft robotics, wearables, energy efficient smart skins and on-demand tunable materials. Canonically speaking, biomimetic samples can be fabricating by partially embedding stiffer plate like segments on softer substrates to create a bi-material system, with overlapping scales. Recent investigations on their mechanics have shown that the origins of many of these behaviors are not merely due to load distribution but because of an intricate interplay of deformation, sliding and interfacial behavior. Such interplay give rise to property combinations that are typically not visible in the parent material of either the scales or the substrates. Here we review and present the origins of some of their fascinating behavior which include nonlinear and directional strain stiffening in both bending and twisting, dual nature of friction which combines both resistance as well as adding stiffness to motion, emergent viscosity in dynamic loading, and non-Hertzian contact mechanics. We will provide derivation of simple mathematical laws that govern structure- property relationships that can help guide design. We will also demonstrate possibilities in non-mechanical properties such as elementary structural coloration and topography influenced mass deposition. We conclude by providing perspectives of future development and challenges.
... We measured morphological features of the tongue that are putatively important to hydrostatic deformation and mucus secretion, as these features are likely to be important for establishing the tongue-prey bond in noniguanian squamates using lingual prey capture ( Figure 1). An explanation of the presumed function of each measurement is provided in Table 2 (see Gilbert, Napadow, Gaige, & Wedeen, 2007;Kier & Smith, 1985;Noel & Hu, 2018;Smith & Kier, 1989 for information on muscular hydrostats). ...
... The tongue is well known to be a muscular hydrostat in many tetrapods (Gilbert et al., 2007;Kier & Smith, 1985;Noel & Hu, 2018;Smith & Kier, 1989), meaning that, due to its constant volume, the incompressibility of intracellular fluid, the orthogonal arrangement of its muscle fibers, and its encapsulation within an elastic, connective tissue membrane, a decrease in one of its dimensions will cause a compensatory increase in other dimensions. In squamates, tongue flicking and lapping, for example, require significant tongue elongation, which is presumed to occur hydrostatically by decreasing tongue diameter to generate an increase in tongue length (Schwenk, 2000a;unpublished data;Schwenk & Wagner, 2001), whereas tongue protrusion during lingual-feeding in iguanians is primarily achieved by means of hyobranchial protraction ( Schwenk & Throckmorton, 1989). ...
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We investigated the functional morphology of lingual prey capture in the blue‐tongued skink, Tiliqua scincoides, a lingual‐feeding lizard nested deep within the family Scincidae, which is presumed to be dominated by jaw‐feeding. We used kinematic analysis of high‐speed video to characterize jaw and tongue movements during prey capture. Phylogenetically informed principal components analysis of tongue morphology showed that, compared to jaw‐feeding scincids and lacertids, T. scincoides and another tongue‐feeding scincid, Corucia zebrata, are distinct in ways suggesting an enhanced ability for hydrostatic shape change. Lingual feeding kinematics show substantial quantitative and qualitative variation among T. scincoides individuals. High‐speed video analysis showed that T. scincoides uses significant hydrostatic elongation and deformation during protrusion, tongue‐prey contact, and retraction. A key feature of lingual prey capture in T. scincoides is extensive hydrostatic deformation to increase the area of tongue‐prey contact, presumably to maximize wet adhesion of the prey item. Adhesion is mechanically reinforced during tongue retraction through formation of a distinctive “saddle” in the foretongue that supports the prey item, reducing the risk of prey loss during retraction. Most scincid lizards use the jaws to capture prey, but the blue‐tongued skink (Tiliqua scincoides) uses its tongue. It employs extensive hydrostatic deformation of its unusually broad tongue to maximize the area of tongue‐prey contact and the strength of wet adhesion.