. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PISCES. 985 which is interposed between the skull and the surface of the brain. Organs of respiration.—The respiration of Fishes is purely aquatic, the oxigenization of the blood being accomplished throughout the entire class by its exposure to the oxygen dissolved in the surrounding medium as it passes through the network of extremely mi- nute vessels that is spread out over the exten- sive surfaces furnished by the gills or branchiae. These organs consist of vascular fringes or laminae placed on each side of the neck,
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. PISCES. 985 which is interposed between the skull and the surface of the brain. Organs of respiration.—The respiration of Fishes is purely aquatic, the oxigenization of the blood being accomplished throughout the entire class by its exposure to the oxygen dissolved in the surrounding medium as it passes through the network of extremely mi- nute vessels that is spread out over the exten- sive surfaces furnished by the gills or branchiae. These organs consist of vascular fringes or laminae placed on each side of the neck, over winch, in the great majority of species, the water taken in at the mouth is made to pass as it issues through the opercular cavities; and in this way the branchial surfaces, being perpetually bathed with aerated water, perform the same office as the lungs of an air-breathing animal. But while respiration is thus accomplished throuehout the whole class by means that are essentially similar, there are several modifica- tions in the mechanical arrangement of the re- spiratory apparatus, each of which will demand our especial notice. Throughout all the extensive division of os- seous Fishes (with the exception of the Lopfio- brancliii) the construction of the breathing organs will be found to accord with the fol- lowing general description. To the external convex surface of each of the four branchial arches (Jig. 522) is attached a double series of flat, elongated, cartilaginous laminae, tapering gradually towards their extremities, the whole forming a crescent-shaped pectinifonn frame- work, over which is spread the highly vascular membrane that constitutes the respiratory sur- face. On making a transverse section of the gill it is found that towards their base, whereby they become attached to the branchial arch (Jig- 520, />), the two series of branchial laminae are united to each other, and, moreover, the structure of each leaflet of the branchia becomes apparent. The
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