The activity of jaw and hyolingual muscles during the entire feeding sequence is examined in the lizard Agama stellio, with special focus on the intraoral transport and swallowing stages, Correlation of electromyography (EMG) data with kinematics shows that the kinematic phases (slow opening, SO; fast opening, FO; fast closing, FC; slow closing/power stroke, SC/PS) are characterised by distinct activities in the jaw and hyolingual muscles. The SO phase is clearly the result of tongue protraction (upon protraction, the tongue is pulled against the prey and consequently the lower jaw is pushed down), whereas the FO phase is caused by activity in the jaw opener and dorsal cervical muscles. Both the FC and SC/PS phases are characterised by pronounced activity in the jaw adductor muscles. Tongue retraction is produced by activity in the hyoid and tongue retractor muscles. A quantitative analysis of time-related EMG data shows that, in accordance with the kinematic analyses, three different stages can be recognised as components of the feeding cycle: prey capture, intraoral transport and swallowing. However, analysis of intensity-related data allowed a fourth stage, crushing, to be detected. Whereas there are indications that prey capture, intraoral transport and swallowing are controlled by different motor patterns, the differences between crushing and transport are likely to be caused by feedback mechanisms. Our results show the importance of including intensity-related data in quantitative analyses of EMG recordings in order to discriminate between feeding stages. Additionally, it is shown that both the jaw and the hyolingual muscles play crucial roles during feeding. During all stages, movements of the hyolingual apparatus are an essential part of the feeding cycle. Thus, when examining lizard feeding mechanisms, the activity patterns of the hyolingual muscles should not be neglected.

The kinematics of prey capture, intraoral transport and swallowing in lizards of the species Agama stellio (Agamidae) were investigated using cineradiography (50 frames s-1) and high-speed video recordings (500 frames s-1). Small metal markers were inserted into different parts of the upper and lower jaw and the tongue. Video and cineradiographic images were digitized, and displacements of the body, head, upper and lower jaw and the tongue were quantified. Twenty additional variables depicting displacements and timing of events were calculated. A factor analysis performed on the kinematic data separates prey capture and swallowing cycles from intraoral transport bites. However, the intraoral transport stage cannot be separated into chewing (reduction) and transport bites. The effect of prey type and size on the feeding kinematics of intraoral transport and swallowing cycles was investigated. During the intraoral transport stage, distinct aspects (e.g. durations, maximal excursions) of the gape and tongue cycle are modulated in response to both the size and type of the prey item. The results for A. stellio generally agree with a previous model, although it is the entire slow opening phase rather than solely the duration of the second part of this phase that is affected by the size of the prey. The intraoral transport cycles in A. stellio show the two synapomorphic characteristics of tetrapods (tongue-based terrestrial intraoral prey transport and the existence of a long preparatory period of prey compression). However, not all five characters of the feeding cycle previously proposed for amniotes are present in A. stellio. One major difference is that in A. stellio the recovery of the hyolingual apparatus does not take place during the slow opening phase but during the slow closing/powerstroke phase.

Muscle function during undulatory swimming is commonly described by the relative timing of muscle activity (EMG) in the strain cycle and has been studied for several fish species, ranging from anguilliforms to carangiforms. This paper supplies the basic data for steady swimming at an intermediate speed in a salamander (Ambystoma mexicanum).The strain cycle of the swimming muscles is estimated using high-speed video recordings (500 frames s(-1)) of an animal swimming in a flow tank. Synchronously, EMG signals of six epaxial myomeres were recorded using bipolar electrodes inserted unilaterally along the body.The neural stimulation pattern is a head-to-tail travelling wave with a higher speed than the kinematical propulsive wave. The resultant phase delay causes a different muscle recruitment pattern along the body axis, similar to reports for anguilliform fishes like the lamprey (WILLIAMS et al., 1989) and the eel (GRILLNER & KASHIN, 1976). The anterior trunk myomeres (up to 45% of the total body length L) are activated purely concentrically (i.e., while shortening). Caudal to the 45% L position, the muscles show an increasing proportion of eccentrical activation.This pattern suggests that there is gross positive work delivery along the body axis, with a limited amount of negative work in the tail tip. This is in agreement with the general conclusions for fish of WARDLE & VIDELER (1994), where this recruitment pattern is associated with a body shape without a distinct tail blade and with direct and continuous thrust production along the body.

Cervical movements during the fast escape head retraction in the pleurodiran turtle Chelodina longicollis were studied by means of x-ray cinematography. Radio-opaque markers were inserted near the cervical joints to allow calculation of joint rotations between the successive vertebrae expressed as a function of time and head position. Head retraction as a percentage of the extended neck configuration and angular and linear velocities were also calculated. A combination of muscular organisation and kinematics shows that the neck is divided into two functional regions, anterior and posterior to the biconvex fifth cervical vertebra respectively. Head retraction proceeds in two phases. During the first phase the animal retracts the head very fast underneath the carapace but leaves the neck partially exposed. This phase (with exception for C3-2 and C5-4) shows no significant differences in the timing of the peak-velocities. During the second phase rotations occur mainly in the proximal joints leading to the maximally retracted configuration. Left and right head retractions are mirror images. Retractions never start from a completely extended neck configuration. Initial angles always occur in C6-5 (joint between vertebrae 5 and 6) and C8-7. These joints are also the major bending sites for full retraction of the neck. Peak-velocities of these joints strongly correlate with each ether but also with head retraction. When expressed as functions of head position, the rotation patterns of the proximal joints are particularly stereotyped. It is hypothesized that both initial angels and stereotypical retraction patterns are required to allow a fast (escape) retraction powered by a simple motor pattern.

Prey capture in Agama stellio was recorded by high‐speed video in combination with the electrical activity of both jaw and hyolingual muscles. Quantification of kinematics and muscle activity patterns facilitated their correlation during kinematic phases. Changes in angular velocity of the gape let the strike be subdivided into four kinematic phases: slow open (SOI and SOII), fast open (FO), fast close (FC), and slow close‐power stroke (SC/PS). The SOI phase is marked by initial activity in the tongue protractor, the hyoid protractor, and the ring muscle. These muscles project the tongue beyond the anterior margin of the jaw. During the SOII phase, a low level of activity in the jaw closers correlates with a decline of the jaw‐opening velocity. Next, bilateral activity in the jaw openers defines the start of the FO phase. This activity ends at maximal gape. Simultaneously, the hyoid retractor and the hyoglossus become active, causing tongue retraction during the FO phase. At maximal gape, the jaw closers contract simultaneously, initiating the FC phase. After a short pause, they contract again and the prey is crushed during the SC/PS phase. Our results support the hypothesis of tongue projection in agamids by Smith ([1988] J. Morphol. 196:157–171), and show some striking similarities with muscle activity patterns during the strike in chameleons (Wainwright and Bennett [1992a] J. Exp. Biol. 168:1–21). Differences are in the activation pattern of the hyoglossus. The agamid tongue projection mechanism appears to be an ideal mechanical precursor for the ballistic tongue projection mechanism of chameleonids; the key derived feature in the chameleon tongue projection mechanism most likely lies in the changed motor pattern controlling the hyoglossus muscle. © 1995 Wiley‐Liss, Inc.

The equilibrium of forces acting on the lower jaw during biting can be assessed by static modelling. Usually, no account is taken for the actual recruitment level of the involved jaw adductors and only one fixed orientation of the food reaction forces is considered. These conditions conflict with reality. Therefore, recruitment levels of eight muscles of Caiman crocodilus are determined by means of quantitative EMG. For 12 crushing bites and one holding bite, these levels were normalized (per muscle) to the maximal activity level ever observed in a total of 72 bites. These activity levels were used as input for a static bite model. A large numbers of simulations are run in which the orientation of the food reaction forces varies over a large range. Several bite points are considered. The model calculates the magnitude of the bite forces and the orientation and magnitude of the joint forces. The results for the individual bites are compared to a model simulation where all muscles are fully active (100%) and to an averaged bite representing a generalized crushing bite of Caiman. This allows to assess the biological meaning of such simulations. It turns out that (apart from the absolute size of the forces) both the 100% model and the generalized bite simulation result in an equilibrium condition which closely approximates the actual in vivo equilibria. Some functional and morphological implications are discussed.

Sexual dimorphism of relative head size is a widespread phenomenon in lizards, males having larger head/trunk ratios than females. In an attempt to explain this sexual dimorphism several hypotheses have been formulated. The two most frequently cited ones are: 1) sexual selection acting on those structures important in intrasexual competition and 2) natural selection for reduction of food competition between the sexes. In the insular subspecies of Podarcis hispanica (P h. atrata) males tend to have significantly larger heads than similarly sized females. We here test an implicit assumption of the dietary divergence hypothesis, namely that an increase in head size results in an increase in gape width and/or bite force, thereby allowing the larger headed sex to exploit larger prey classes. Using a static bite force model, we calculated the magnitude of bite forces for given directions at given positions on the jaws and for different head sizes. We experimentally determined the hardness of three different prey items and compared the data to the maximal bite force produced by both sexes. Our results suggest an important difference in male and female bite capacity, which may bear significant ecological relevance, and are in agreement with the implicit assumption of the dietary divergence theory.

Analysis of the feeding kinematics of Astatotilapia (a small cichlid fish) suggests the presence of peripheral feedback modulation of the motor pattern, allowing the act of suction to be abbreviated. In this way, the effort spent in suction is minimized. The biological significance of the development of such a modulating feedback system is not immediately obvious from a 'classical ecological' point of view. It is postulated that the muscular metabolism itself might constrain the short, transient and strenuous motor output typical of suction feeding. Thus, reducing the suction effort makes sense when successive strenuous head-part movements are immediately required for additional suction, buccal transport or spitting. This hypothesis was tested by in vivo electrical stimulation of muscles important in feeding: the epaxials, which lift the skull and expand the buccal cavity. Reliable stimulation variables for the epaxial muscles were determined from preliminary stimulation experiments and from electromyographic recordings of these muscles in a specimen feeding on crickets. Stimulation trains of variable duration (<150 ms) were applied in series of five trains. The intervals between trains were variable as well (<1 s). The mechanical output was measured by means of an accelerometer, a force transducer or a magnetoresistive displacement transducer. In the latter case, the time course of the mechanical output could be recorded and analysed. The hypothesis predicts a decrease in the muscular output with increasing effort (long trains) and fast repetition (short intervals). The experimental results show the expected decline in mechanical output from one stimulation train to the next when longer stimulation bursts are imposed in quick succession. Statistical analyses (multiple regression) showed that train length, train rate and train number contribute significantly to the observed variation in mechanical output, supporting the hypothesis. Explanations for the phenomena are discussed.

Movements of the neck, jaws, and hyolingual apparatus during inertial feeding in Caiman crocodilus were studied by cineradiography. Analysis reveals two kinds of cycles: inertial bites (reposition, kill/crush, and transport) and swallowing cycles. They differ in their gape profile and in displacement of the neck, cranium, and hyolingual apparatus.Inertial bites are initiated by an elevation of the neck and cranium; the head is then retracted backward, the prey simultaneously being lifted by the hyolingual apparatus. Next the lower jaw is depressed, and the prey is rapidly pushed further upward by the hyolingual apparatus. Thereafter fast mouth-closure occurs with the neck and cranium being abruptly depressed, the lower jaw elevated, and the hyolingual apparatus rapidly retracted ventrally. Depression of the neck and cranium thrusts the head forward and impacts the backward moving prey more posteriorly in the oral cavity.Swallowing cycles initially involve movement of the hyoid in front of the prey followed by rapid posteroventral retraction of the hyoid, forcing the prey into the esophagus during opening and closing of the mouth. After mouth-closure, the hyoid apparatus is again protracted.Jaws, neck, tongue, and hyoid apparatus play an active role during inertial feeding sequences. At the beginning of a feeding sequence, the hyolingual apparatus mainly moves dorsoventrally, whereas toward the end of a sequence anteroposterior displacements of the hyoid are prominent.

Analysis of lateral radiographic films reveals that the upper and lower pharyngeal jaws in Haplochromis burtoni (GUNTHER, 1893) show opposite anteroposterior displacments during food reduction. Force is generated during upper jaw retraction by elevation and slight protraction of the lower pharyngeal jaw (compression phase) and subsequently by depression and strong protraction of the lower jaw (shearing phase). These results contradict previous findings in which the upper and lower pharyngeal jaws show synchronous protraction and retraction.

Routine histochemistry was used to study fibre type composition of the masticatory muscles of the frugivorous flying fox, Pteropus giganteus (BRUNNICH, 1782). Frozen sections were stained for alkaline- and acid-stable ATPase, NADH-tetrazolium reductase and alpha-glycerophosphate dehydrogenase, and fibres were subsequently identified as slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG) and fast-twitch glycolytic (FG). Based upon relative proportions of fibre types, muscles and their subdivisions can be classified into three groups: group 1 muscles (superficial and medial temporales), containing less than 10 % of SO fibres, group 2 muscles (superficial and deep masseter, zygomaticomandibularis, deep temporalis, medial pterygoid), containing 20-30 % of SO fibres, and group 3 muscles (anterior and posterior digastrics), containing 30-50 % of SO fibres. Moreover, in group 3 muscles less than 5 % of the fast twitch fibres are fatigue resistant (FOG), whereas in both group 1 and 2 muscles, about 20-30 % of the fast-twitch fibres are FOG. The histochemical profile of the masticatory muscles is correlated directly with their contraction characteristics and indirectly with their EMG patterns.

Analysis of lateral and dorsoventral radiographic films shows that ingestion, transport, and mastication in Pedetes capensis (Rodentia) are cyclic and their movement patterns are essentially similar for the three food types offered. During the ingestion cycle, closing of the mouth is accompanied by a backward translation of the condyles, so that movement is predominantly orthal. During the opening stage, the extent of the anterior condylar translation is smaller. As a result the mandibular incisors move ventrally and posteriorly. During the ingestion cycles, food is transported to the back of the tongue, with the transverse rugae and the folds of the upper lip playing important roles. Springhares show a bilateral masticatory pattern; food is chewed on both sides simultaneously. During chewing, the condyles lie in their most forward position at maximum opening of the mouth. The mouth is closed by rotation of the lower jaw around the temporomandibular joint coupled with posterior condylar translation. At the beginning of the slow-closing stage, the upward rotation of the mandible slows and the jaw slowly shifts forward. During the grinding stage, the mandible is shifted forward with both toothrows in occlusion. During the opening stage, the jaw returns to its starting position. Comparison of kinematic and anatomical data on rodent mastication suggests that some dental characteristics form the most important factors regulating the masticatory pattern and consequently allow reasonably reliable prediction of rodent masticatory patterns.

Jaw mechanics in Pteropus were studied by means of a three‐dimensional model. The model included several parameters of muscle architecture, combined with quantified movement and electromyographical data. Estimates of the nature of the applied forces that act upon the mandible during a chewing cycle, and subsequent estimates of reaction forces at the bite point and joints during the powerstroke, were thus obtained for different food consistencies. The resultant muscle force (relative to the palate) shifts from upward and slightly backward at large gapes to upward and markedly backward at the end of closing. The resultant simultaneously moves anteriorly. During the powerstroke it retains a constant position and orientation along the thickened anterior edge of the coronoid process. The early stages of opening are guided by the slope of the teeth and mandibular fossa; during the remaining part of opening the working line of the resultant crosses the skull behind the joint and thus acquires an opening moment. The bite force has downward and forward components, and a slight transverse component. For a given applied muscular force its magnitude is larger in more posteriorly positioned bite points. Both joints are loaded, the contralateral one more than the ipsilateral. Food consistency affects magnitude and orientation of the applied force, and hence, magnitude and orientation of the bite force and magnitude of the joint reaction forces. The magnitude of masseter activity relative to temporalis activity appears to be the key factor for the orientation of the bite force, and hence for the mechanical optimal position of the food. The adaptive value of the general topography of the masticatory muscles in Pteropus is discussed.

Springhares, Pedetes capensis, are adapted for nocturnal life in arid and semiarid regions. Their large orbits and acoustic apparatus differ greatly from the primitive conditions for rodents. Herein, the masticatory apparatus of springhares is compared with the scarce data available for protrogomorph, myomorph, and hystricomorph rodents. The muscles of the zygomasseteric complex are of the hystricomorphous type and show an extremely strong development (87.5% of the total mass of the adductor muscles) compared to the hystricognathous hystricomorphous rodents (66.4% in Cavia). The digastric muscle and the medial pterygoid, in contrast, are of the sciurognathous type. Within each evolutionary line the musculature differs only in detail, whereas masticatory movement patterns vary significantly. Apparently, skeletal elements of the masticatory apparatus significantly affect the movement pattern of the lower jaw during the power stroke during which the molar teeth come into occlusion.

Mastication has been studied by cinematography and quantitative electromyography while flying foxes, Pteropus giganteus, were freely feeding on standardized pieces of apple, soaked raisin, and banana. The primarily orthal mandibular movements are caused by mainly bilaterally symmetrical firing of all the masticatory muscles. Asymmetric activity in the superficial and deep masseter and medial pterygoid causes slight protrusion early in opening. Slight lateral deviations at the end of opening and at the start of closing are caused by asymmetric and asynchronous activity in the pterygoids and digastrics, and by asynchronous firing of the deep temporalis and zygomaticomandibularis. Food consistency affects movement characteristics as well as characteristics of muscular activity. In this study electromyograms were digitized and the number of spikes and mean amplitude per interval (set by the filming rate) recorded. Although a significant correlation exists between descriptors, the product thereof appears to be the best predictor of certain kinematic variables (cycle length and maximum excursion of the mandible). On the other hand, the changes in magnitude of muscular activity as a function of the position of a cycle in the reduction sequence and as a function of food consistency are more translated in a variation of the mean amplitude than in a variation of the number of spikes per interval. Observed variation differs among muscles studied. It is most apparent in the superficial and deep masseter and least in the temporalis and zygomaticomandibularis. Late cycles of apple and raisin mastication are long and exhibit large gapes but almost no anterior movement. The adductor activity frequently shows a synchronized, pulsatile pattern leading to an unfused tetanus.