The common frog . of small membranous structures only. The term skeleton, however, should properly in-clude all the membranous and gristly, as well as thebony structures.^ Moreover, more or less of the skinmay attain to so solid a condition as to justify itscomprehension under the name skeleton, even inthe popular signification of that term. The skin of Vertebrate animals consists of two layers : an outer layer (the epidermis or ecteTon), andan inner layer (the dermis ox enderori). 1^\\q epidermis,and any projections or processes developed from itwhen they take on a dense or hardened structure
The common frog . of small membranous structures only. The term skeleton, however, should properly in-clude all the membranous and gristly, as well as thebony structures.^ Moreover, more or less of the skinmay attain to so solid a condition as to justify itscomprehension under the name skeleton, even inthe popular signification of that term. The skin of Vertebrate animals consists of two layers : an outer layer (the epidermis or ecteTon), andan inner layer (the dermis ox enderori). 1^\\q epidermis,and any projections or processes developed from itwhen they take on a dense or hardened structure,become horny. Of such horny nature are hairs,feathers, nails, and scales ; they are more or lessepidermal appendages. The der^nis when hardenedbecomes bony, and of such nature are the bony skin-plates or scutes and teeth. They are dermal * See Lessons in Elementary Anatomy, Lesson II., p. 22. VI.] THE COMMON FROG. 6i appendages. Now both layers of the skin of thecommon Frog are entirely soft and utterly destitute. Fig. 26.—Dorsal surface of the Cara^jace ot a Fresh-water Tortoise (Emys). 1—8,expandf-d neutral spires ; r^—>^, expanded ribs ; mi, first median (or nuchal)plate \ py, last median (or pygal) plate; m, marginal scutes. The dark linesindicate the limns of the plates of the horny epidt-rmal tortoise-shell; the thinsutures indicate the lines at ihe junction of the bony scutes.
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherlondo, bookyear1874
