The anatomy of the buccal mass and the function of nine principal muscle groups involved in the feeding movements, are described for the mollusc Tritonia hombergi. Anatomical and physiological studies on some 40 neurones along the posterior border of the buccal ganglia indicates that many are primary motoneurones to the muscles of the buccal mass. The feeding cycle may be divided into three phases of muscle activity termed Protraction, Retraction and Flattening, which are correlated with the patterned bursting observed in P, R and F motoneurone groups within the motoneurone population. A fourth group of motoneurones are thought to innervate muscles to the outer lips which are active during protraction. The patterned output of impulses in the buccal nerves during feeding cycles confirms that the motor control of the muscle groups may be explained in terms of the sequential activation of the P, R and F cells.

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