The bones, muscles, and connective tissue elements constituting the head of Perca fluviatilis L. are described. Electromyographic techniques were applied to investigate muscle activity. Details of the experimental set-up are given. Cine film made it possible to analyse the movements. Radiological techniques were also applied. A method for synchronizing EMGs and films is described. The use of EMGs for determining mechanical parameters of contracting muscles is considered in relation to the findings reported in the literature. Three types of movements, respiratory, coughing and feeding were studied. 2. During respiration, activity is recorded from most of the muscles of the head but not in some parts of the m. add. mandibulae or in the sternohyoid muscle. The head muscles can be divided into two groups, one of which is active during inspiration, the other during expiration. Evidence from EMGs and from stimulation experiments has provided experimental proof that depression of the lower jaw during respiration is caused by contraction of the mm. levatores operculi. The two parts of the geniohyoid muscle are active in different phases of the respiratory cycle; this fact is discussed. The results are compared with the data in the literature. 3. Recordings of the muscles during coughing movements have been combined in a diagram. These movements of the various parts of the head are also shown graphically. A cough can be divided into three phases, phase 1, an interphase, and phase 2. The mouth is closed at the beginning of the interphase then rapidly opened and again closed in phase 2. A cleaning function of the cough is not considered to be very probable; it seems more likely that coughing is evoked by stress situations. 4. EMGs of feeding movements are shown. A diagram of the muscle activity during feeding is presented. All the head muscles and also some trunk muscles are involved in the feeding movements. The amplitude of the feeding EMG is 4 to 10 times greater than during movements related to other functions. The expansion and elongation of the buccal cavity during feeding movements produce a suction force. The velocity of the water flowing into the buccal cavity and the negative pressure inside the buccal cavity are calculated. The connection between the muscle activity and changes in the position of parts of the head is analysed (e.g., the activity of both the geniohyoid muscles during the expansion phase for the depression of the lower jaw). The contraction of the dorsal and ventral body musculature causes a rotation of the working line of the sternohyoid muscle, thus adding a ventral component to the force exerted by the latter on the hyoid arch. Feeding movements differ in many respects (e.g., the activity of the trunk muscles, the contraction of the whole m. add. mandibulae) from respiratory movements, and they must be regarded as a separate complex of events. 5. Subdivision of the head into functional components shows a high degree of overlap between these components. The dominant function, i.e., feeding, makes the greatest demands on the structures. Partially contradictory requirements of different functions have resulted in compromise situations. Structural adaptations related to the demands of the feeding function are discussed (for example: the folded sheets of connective tissue between premaxillae, maxillae, and lacrimals; the branchiospinae on the first ceratobranchials; the ligament connecting the medial side of the lower jaw with the proximal ends of the branchiostegal rays). The structure of some muscles was found to be partly predictable on the basis of architectural considerations and the available information about muscle-tendon systems. The shape of the hyomandibula is discussed in relation to the muscle forces acting on it. More insight into the selective forces that have played a role in the evolution of the perch was obtained.
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J.W.M. Osse (1968) studied this question.