Page:Natural History (1848).djvu/109

Rh paddle or oar, to be worked in a medium of great density, and hence the shoulder blade is of remarkable breadth, and the other bones solid and powerful.

FIN OF DOLPHIN.

The hind limbs we observed in the Seals placed very far behind, and forming two fan-shaped oars, whose direction was backward. In the Whales these limbs are altogether wanting (or are represented by one or two small pelvic bones, isolated in the flesh); but they are replaced by a broad cartilaginous fin at the extremity of the body, placed not vertically, as in the Fishes, but horizontally. This organ is the chief instrument of motion, which is mainly performed by alternate strokes upward and downward, rendered effective by its immense muscular power. In some of the larger Whales this caudal fin is upwards of twenty feet wide, and contains a hundred superficial feet.

The head is joined to the trunk without any contraction, so that the neck seems to be altogether wanting; the seven vertebræ, however, that belong to this part of the skeleton in all Mammalia, are present, but are so narrow, and so soldered together (anchylosed) as to appear like a