. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCH FISHES 155 PRODUCTION OF RESPIRATORY CURRENT For tlie sharks and rays in general the respiratory current is produced by the interaction of the complicated series of buccal and ])haryngeal muscles which insure that when the current enters the mouth the external clefts close and when the clefts oi)en. the mouth closes. In general the action is as follows: By the contraction of the ventral, longitudinal, or hyj^obranchial musculature. Fig. 148. A. Part of a gill pocket of Cetorhinus. (From Pavesi.) B. Diagram of a section parallel to the
. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCH FISHES 155 PRODUCTION OF RESPIRATORY CURRENT For tlie sharks and rays in general the respiratory current is produced by the interaction of the complicated series of buccal and ])haryngeal muscles which insure that when the current enters the mouth the external clefts close and when the clefts oi)en. the mouth closes. In general the action is as follows: By the contraction of the ventral, longitudinal, or hyj^obranchial musculature. 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).. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Daniel, J. Frank (John Franklin), 1873-1942. Berkeley,Calif. , University of California press
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