SYNOPSIS.

SYNOPSIS. Previous research indicated that the evolution of feeding motor patterns across major taxonomic assemblages might have occurred without large modifications of the manage of the jaw and hyolingual muscles. However, the proposal of this evolutionary scheme was hampered by way of the lack of data for a key taxa such as lizards. latter data on jaw and hyolingual feeding motor patterns of a number of lizard families glance at extensive variability within and among species. Although greatest in number lizards respond to changes in the structural properties of cheer items by modulating the activation of the jaw and hyolingual muscles, a certain quantity of food specialists might have dissipated this ability. Whereas the overall similarity in motor patterns across different lineages of lizards is large for the hyolingual muscles, jaw muscle activation patterns appear to be to be more flexible. Nevertheless, all data recommend that both the jaw and hyolingual regularity are complexly integrated. The elimination of feedback pathways from the hyolingual rule through nerve transection experiments clearly displays that feeding cycles are largely shaped from feedback interactions. Yet, novel motor patterns including unilateral regulate seem to have emerged in the evolution from lizards to snakes.

INTRODUCTION The vertebrate head is a textbook example of a webwork integrated system, where one function cannot be optimised without potentially compromising others (Lauder, 1989) In addition to being a major information gathering and processing middle immensly diverse functions such as feeding, breathing, drinking, display, and in many tetrapods also vocalisation, have to be performed by the agency of the same elements. Yet, these diverse functions can merely be performed through the interplay between the jaw and hyolingual methods Both these systems are complicate units composed of a large number of muscles attached to bony or cartilagenous natural mediums Moreover, as the hyolingual apparatus is a musculoskeletal scheme suspended between the jaws and the pectoral girdle, the potential number of ranks of freedom is enormous. To add to this complexity, the couple systems are largely innervated by means of different pathways. Whereas the jaw adductor a whole in lizards is mainly innervated by way of the trigeminal and facial powers (providing both motor input and sensory afferents), the hyolingual body is mainly supplied by the glossopharyngeal (largely sensory), hypoglossal (predominantly motor input) and first spinal vigors (motor input into the hyoid retractors; Willard, 1915; Oelrich, 1956; Meyer and Nishikawa, 2000) Direct connections between the sum of two units systems exist, as the mandibular ramus of the n trigeminus provides motor input into the m intermandibularis (running inbetween the brace rami of the lower jaw) and branches disclosed into the tongue functioning as sensory afferent and physically connecting to the N hypoglossus. Feedback from the visual, olfactory, gustatory, vomeronasal and somatosensory (eg muscle spindles, joint receptors) theorys are also important in assuring optimal feeding.

Given this structural complexity, the bridle of the feeding apparatus is a involved task which appears to require continuous on-line reign over Yet, for cyclical systems in general, a simple neuromotor steering based in succession a centralised pattern generator (or a stake of coupled CPG's) is notion to exist, thus largely simplifying have charge of (e.g., Grillner and Wallen, 1985; Szekely 1989) Although this paradigm is largely based forward studies on the locomotor apparatus, a similar command paradigm is usually put forward for mammalian chewing round of yearss (Thexton, 1974, 1976; Dellow, 1976) In accordance with this theoretical framework, it has been moveed that in lower tetrapods too, the feeding round of yearss might be driven by fairly simple motor pattern generators or neural oscillators (Bramble and Wake, 1985)

Based forward the large similarities between lower tetrapod and mammalian feeding revolution of times it was hypothesized that the evolution of feeding motor patterns across major taxonomic clusters might have occurred without large modifications of the central pattern generators) controlling the jaw and hyolingual muscles (Bramble and Wake, 1985) The basic ingredients of the lower tetrapod feeding period were summarised in a theoretical gauge feeding cycle which was hypothesised to give an account of the primitive tetrapod condition. In analogy to the mammalian feeding period the model feeding cycle was subdivided into five distinct phases: the heavy opening of the jaws (I and II), fast opening, fast closing and a gradual closing/ power stroke. Muscle activation patterns associated with these kinematic units were propos as well. Whereas the moderate opening phase was thought to be caused by means of an activation of the jaw opener intrinsic tongue muscles, the intermandibularis clump and the tongue and hyoid protractors, during fast opening coactivation of the cervical epaxial musculature, the jaw opener and hyoid retractors was look fored to occur. Jaw closing onward the other hand was musing to be associated with activity in the hyoid retractors (fast closing), jaw adductors and potentially the jaw opener (Bramble and Wake, 1985)