. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 102 COMPARATIVE ANATOMY. became bent downwards, and thus the angle between it and the median plane of the trunk was gradually reduced, until in Mammals eventually, the longitudinal axis of the limb, when at rest, came to lie parallel with the median plane of the body. In the higher types this is more particularly the case as regards the posterior extremities, the anterior undergoing the most varied adaptations and modifications, and giving rise to tactile, prehensile, or flying organs, or, as in
. Elements of the comparative anatomy of vertebrates. Anatomy, Comparative; Vertebrates -- Anatomy. 102 COMPARATIVE ANATOMY. became bent downwards, and thus the angle between it and the median plane of the trunk was gradually reduced, until in Mammals eventually, the longitudinal axis of the limb, when at rest, came to lie parallel with the median plane of the body. In the higher types this is more particularly the case as regards the posterior extremities, the anterior undergoing the most varied adaptations and modifications, and giving rise to tactile, prehensile, or flying organs, or, as in aquatic Mammals, becoming once more converted into rowing organs. Thus we may also reduce the limbs of all the higher Vertebrata to a single ground-type, and we may further connect the latter with the fin of Fishes by taking the ground-plan of the fin of Ceratodus and Elasmobranchs, consisting of a main axis and lateral rays, as a starting-point. Figs. 87 and 88 will render this statement clear. In Fig. 88, a thick line is seen beinnin at //, and passing through F, i, c, c, 2, to //. This is the main. Fiu. 87.—DIAGRAMMATIC FIGURES TO snow THE DELATIONS OF THE FREE EXTREMITY TO THE TRUNK IN FISHES (A), AND THE HIGHER VKTEBRATES (B). S, pectoral arch ; Mt, metapterygium, which corresponds to the main uluar ray (Ui); lid, secondary radial ray. axis, and from its proximal end (at //) a lateral ray passes off through T, t, to /. A second series of lateral rays arises from the other side of the axis. Thus we have here also the primitive biserial form, with a marked preponderance of one row of radii. At the same time it must be borne in mind that this arrange- ment of radii on an axis is less plainly seen in the embryonic con- dition than in the adult limb, and we must therefore speak of the relations of these parts as similar rather than as strictly homologous. The fore- and hind-limbs show a great similarity as regards the form and position of their various parts. A division into
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