CREATION BY EVOLUTION
these strong-jawed, pike-like fishes each of the stout paired fins (corresponding to our arms and legs) was supported by an internal skeleton consisting of bony rods converging toward a single bone, corresponding respectively to our single upper arm bone (the humerus) or to our thigh bone (the femur). The fore paddles were supported by a complex shoulder girdle, parts of which correspond to our collar and shoulder bones; the hind paddles were supported on a bony plate corresponding to the lower bars of our pelvis.
The skull of these lobe-finned ganoids, like the human skull, was a complex of two very distinct sets of elements. The inner skull, or braincase, consisted of the bony trough surrounding the brain and of the bony shells or capsules surrounding the organs of smell, sight, and balance. The outer skull consisted of a shell of bones, derived, like the scales on the body, from the skin. In the earlier crossopts (such as Osteolepis) the outermost layer of the bony skull and scales consisted of a hard, shiny, porcelain-like substance called ganoin, but in many of the later crossopts this outer layer was lost, leaving a sculptured bony surface.
Among living fishes only the famous Polypterus, the bichir of the Nile, and a nearly related genus have any claim to be considered the modified descendants of these lobe-finned or crossopt fishes of the Devonian period. These interesting relics still retain vestiges of former air-breathing arrangementsin their lungs or swim-bladders, but they now rely chiefly on their gills for aeration.
Origin of the Amphibia
The connecting links between the lobe-finned fishes and the amphibians of the coal forests are not yet discovered, but all the known earlier land-living forms agree in so many points of structure with the lobe-finned fishes that there can
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