The Probert Encyclopaedia of Nature

FIN

Fins are the projecting- wing-like organs which enable fishes to balance themselves and assist in regulating their movements in the water. The fin consists of a thin elastic membrane supported by rays or little bony or cartilaginous ossicles. The pectoral or breast fins are never more than two; they are placed immediately in the rear of the gill-opening on the shoulder. In a state of rest these fins are parallel with the body, and have the apex towards the tail. The ventrals, or abdominal fins, are placed under the throat or belly, and point downwards and backwards. They are smaller, in general, than the pectorals, and have sometimes long appendages. Those of the back, or the dorsal fins, point upwards and backwards, and vary in number from one to four, to which sometimes are added several finlets or pinnuioe - small appendages which are seen in the mackerel. The anal fins are situated behind the vent, varying in number from one to three, placed vertically, and, like the dorsal, generally deeper on the anterior margin. The caudal, or tail fin, terminates the body, and both propels the fish and serves as the rudder by which it steers itself. The pectoral and ventral are known as paired fins, and represent the fore and hind limbs of other vertebrates; the dorsal, anal, and caudal are median, vertical, or unpaired fins, and are organs peculiar to fishes.
Research Fin