QUANTITATIVE-ANALYSIS OF JAW AND HYOLINGUAL MUSCLE-ACTIVITY DURING FEEDING IN THE LIZARD AGAMA-STELLIO

The activity of jaw and hyolingual muscles during the entire feeding s equence is examined in the lizard Agama stellio, with special focus on the intraoral transport and swallowing stages, Correlation of electro myography (EMG) data with kinematics shows that the kinematic phases ( slow opening, SO; fast opening, FO; fast closing, FC; slow closing/pow er stroke, SC/PS) are characterised by distinct activities in the jaw and hyolingual muscles. The SO phase is clearly the result of tongue p rotraction (upon protraction, the tongue is pulled against the prey an d 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 t he jaw adductor muscles. Tongue retraction is produced by activity in the hyoid and tongue retractor muscles. A quantitative analysis of tim e-related EMG data shows that, in accordance with the kinematic analys es, three different stages can be recognised as components of the feed ing cycle: prey capture, intraoral transport and swallowing. However, analysis of intensity-related data allowed a fourth stage, crushing, t o be detected. Whereas there are indications that prey capture, intrao ral transport and swallowing are controlled by different motor pattern s, the differences between crushing and transport are likely to be cau sed by feedback mechanisms. Our results show the importance of includi ng intensity-related data in quantitative analyses of EMG recordings i n order to discriminate between feeding stages. Additionally, it is sh own that both the jaw and the hyolingual muscles play crucial roles du ring feeding. During all stages, movements of the hyolingual apparatus are an essential part of the feeding cycle. Thus, when examining liza rd feeding mechanisms, the activity patterns of the hyolingual muscles should not be neglected.