. Animal biology. Zoology; Biology. C ^ Three parts of pterygium Ulna Pectoral arch. Humerus Radius Me tap ferygium Fig. 246.—Diagrams to illustrate the theoretical change of a fin into a limb. A, pectoral fin of Ceratodus, an extinct dipnoan, representing a primitive fin. B, pectoral fin of Polypterus, a lobe-finned ganoid, or crossoptcrygian, now living. C, D, E, hypothetical changes from A to B. F, pectoral fin of a pro-amphibian, a hypothetical form intermediate between Polypterus and an amphibian. G, condition in amphibian, (A, B, F, and G from Wiedersheim, " Ve
. Animal biology. Zoology; Biology. C ^ Three parts of pterygium Ulna Pectoral arch. Humerus Radius Me tap ferygium Fig. 246.—Diagrams to illustrate the theoretical change of a fin into a limb. A, pectoral fin of Ceratodus, an extinct dipnoan, representing a primitive fin. B, pectoral fin of Polypterus, a lobe-finned ganoid, or crossoptcrygian, now living. C, D, E, hypothetical changes from A to B. F, pectoral fin of a pro-amphibian, a hypothetical form intermediate between Polypterus and an amphibian. G, condition in amphibian, (A, B, F, and G from Wiedersheim, " Vergleichenden Anatomic der Wirheliiere"; C to E, from Kingsley, "Outlines of Comparative Anatomy of Vertebrates," by the courtesy of P. Blakiston's Son & Co.) second becomes an aortic arch, through which the blood passes to the trunk and tail; the third disappears; and the fourth, in part, becomes the basal portion of the pulmonary artery leading to the lung. A cutaneous branch of this fourth arch also becomes developed in an amphibian when it breathes through the skin. The heart becomes three- chambered, the single auricle of the fish being divided in the amphibian into a right auricle which receives the blood from over the body and a left auricle which receives the blood returned from the lungs. The ventricle remains single and serves to send out blood both to the systemic and to the pulmonary circulation, but its walls become thrown into folds which prevent a complete mixing of the arterial and venous blood. A fourth change is incident to the use of the limbs to support the body and to serve as locomotor appendages on land. Paddle-like. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wolcott, Robert Henry, 1868-1934. New York ; London : McGraw-Hill Book Company, Inc.
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