The Muscular Basis of the Respiratory Pumps in the Trout

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Abstract
An account is given of the muscles and skeleton of the trout head and of the mechanisms coupling the different functional components of the skull. The activity of the main respiratory muscles has been recorded electromyo-graphically and simultaneously with pressure and movement recordings from the buccal and opercular cavities. The muscles may be divided into two main groups according to whether they are active during the expansion or contraction phase of the pumps. The protractor hyoideus (geniohyoideus) was found to be active only during the contraction phase. There are differences in the muscles that are active, depending upon the depth of ventilation. Shallow ventilation is maintained by the adductor mandibulae, adductor arcus palatini et operculi, and levator hyomandibulae et arcus palatini. During deeper ventilation the stemohyoideus, protractor hyoideus and hyohyoideus muscles come into action. Only during strong ventilation does contraction of the dilator operculi play a part in opercular abduction. There are variations in the pattern of muscular activity in different individuals and also in the same individual at different times. Such differences in muscular activity are not clearly reflected in the movement and pressure recordings, because of the complex couplings between different parts of the pumping mechanism. As contraction of most muscles affects both the opercular and buccal cavities it is concluded that a model of teleost ventilation based upon a double pumping mechanism must incorporate the couplings between these pumps.