Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . y bear the name of inter-spinous bones; and when a still greater lengthof osseous support is wanted, new centres ofossification are developed at their extremities,giving rise to a series of additional pieces, joinedend to end, and carrying out the interspinous MUSCULAR SYSTEM OF FISHES. 425 bone, and the ray which terminates it, to a con-siderable distance. This structure is distinctlyseen in the small dorsal fins of the anal fins, which are situated on the lowerside of the bod
Animal and vegetable physiology, considered with reference to natural theology, by Peter Mark Roget .. . y bear the name of inter-spinous bones; and when a still greater lengthof osseous support is wanted, new centres ofossification are developed at their extremities,giving rise to a series of additional pieces, joinedend to end, and carrying out the interspinous MUSCULAR SYSTEM OF FISHES. 425 bone, and the ray which terminates it, to a con-siderable distance. This structure is distinctlyseen in the small dorsal fins of the anal fins, which are situated on the lowerside of the body, in the vertical plane, and nextto the tail, are, in like manner, supported byrays, having the same parallel, or fan-like arrange-ment as the preceding. The caudal fin, or ter-minal expansion of the tail has also a similarstructure. The muscles of fishes compose a large portionof the bulk of the body, but they are arrangedin a less complex manner than those of the ani-mals of the higher classes. Those which appearimmediately underneath the integuments areshown in Fig. 194, where m, m are the great. lateral muscles, producing the flexion of thebody and tail: d is the dorsal fin, which israised by the muscle d; p, the pectoral fin,expanded by the muscle p : v, the ventral fin,moved by the muscles situated at v : a, the analfin, in like manner moved by muscles at itsbase a: and c, the caudal fin, the muscles for 426 THE MECHANICAL FUNCTIONS. moving which are seen at c: o is the opercu-lum, or flap, which covers the gills: and n, thenasal cavities, or organs of smell. The form ofthe body, and disposition of the skeleton, allowof their being inserted immediately on the partswhich they are intended to approximate. Hencethe use of long tendinous chords is dispensedwith.* The actions of the muscles are easily under-stood from the nature of their insertions. Ingeneral, the direction of the fibres is in somedegree oblique, with reference to the motionperformed. Two series of muscles ar
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