History of the human body / by Harris Hawthorne Wilder.

  • Harris Hawthorne Wilder
Date:
1909
Catalogue details

Licence: Public Domain Mark

Credit: History of the human body / by Harris Hawthorne Wilder. Source: Wellcome Collection.

    49/620 (page 31)
    Gymnopliiona, which still possess scale rudiments, not visible externally. The Stegocephali are of extreme importance, since they were the ancestors both of the present-day amphibians and of the two main reptilian lines, and the survival of a single representative would have been of priceless value to mor¬ phologists. As it is, however, we are in possession of a large number of fossil remains, many of them extremely well pre¬ served, and representing four distinct orders; and further dis¬ covery along this line may well be expected at any time. Of the soft parts the fossil imprints furnish but little evidence, a lack which must be supplied by the study of the urodeles, undoubtedly their nearest living allies and presumably not very different in the essential internal features. These latter animals, though not quite in the direct line of human ancestry, are thus of the greatest importance as the best representatives of what may be called the amphibian stage. The urodeles comprise the tailed amphibians, their most typical representatives being the forms known as sala¬ manders and newts, also in many sections, unfortunately, “ lizards,” owing to their superficial resemblance to these latter animals. The more primitive members of this group are often large (10-40 cm.), and the giant Cryptobranchus of Japan, the largest of all living amphibians, attains the length of a meter. The Anura, or tailless amphibians, include frogs, toads and tree-toads, and attain their tailless condition in part by a retrogressive development of the caudal region and in part through the excessive development of the ilia and the thigh muscles, a feature connected with their jumping habits. The Gymnophiona are blind subterranean forms, burrowing in the earth like earth-worms, to which they bear considerable re¬ semblance. They are much attenuated, are without external limbs, and have their bodies clearly marked off into annular segments. They occur only in the warmer parts of the world and consist of but few forms. Arising also from the Stegocephali come the reptiles, which have apparently developed along two lines, the one leading to