. The elasmobranch fishes . Fig. 148. A. Part of a gill pocket of Cetorhinus. (From Pavesi.) B. Diagram of a section parallel to the gill rakers. &./•., branchial ray; fl., filaments; , gill rakers; , gill pocket; ia., internal branchial aperture. the floor of the mouth and pharynx is lowered, thus enlarging the Ijuccal and pharyngeal rooms, at the same time that the mouth is opened. Into this cavity the water rushes. The adductors then act, closing the mouth and at the same time flexing the epi- and ceratobranchial segments of the arches, thereby spreading apart the cartilaginous
. The elasmobranch fishes . Fig. 148. A. Part of a gill pocket of Cetorhinus. (From Pavesi.) B. Diagram of a section parallel to the gill rakers. &./•., branchial ray; fl., filaments; , gill rakers; , gill pocket; ia., internal branchial aperture. the floor of the mouth and pharynx is lowered, thus enlarging the Ijuccal and pharyngeal rooms, at the same time that the mouth is opened. Into this cavity the water rushes. The adductors then act, closing the mouth and at the same time flexing the epi- and ceratobranchial segments of the arches, thereby spreading apart the cartilaginous branchial rays and causing the pockets to enlarge. The water now enters the pockets and is then forced out through the external clefts by the contraction of the constrictor and interbranchial muscles. By this action of the muscles a rhythm is produced which under conditions of rest is about thirty-five respirations a minute (Heterodontus francisci).
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