A treatise on zoology . oubtless derived mainly fromthat bud the position of which it continues to occupy throughoutdevelopment, and the radial muscles correspond in number andrelative position to the buds from which they have been formed(Figs. 47, 51). In this respect also the median resemble the pairedfins. Indeed, it is very dou))tful whether any fusion of neighbouringbuds takes place at all in such low forms as the Elasmobranchs 78 PAIRED FINS h2,^ ^ V I I t^ y ^ = E = ils,i *^ £ mM ss ^ i - J 05 «> fe p e g-. « it o *^ S >- PAIRED FINS 79 (Goodrich [176]), and there is evidence
A treatise on zoology . oubtless derived mainly fromthat bud the position of which it continues to occupy throughoutdevelopment, and the radial muscles correspond in number andrelative position to the buds from which they have been formed(Figs. 47, 51). In this respect also the median resemble the pairedfins. Indeed, it is very dou))tful whether any fusion of neighbouringbuds takes place at all in such low forms as the Elasmobranchs 78 PAIRED FINS h2,^ ^ V I I t^ y ^ = E = ils,i *^ £ mM ss ^ i - J 05 «> fe p e g-. « it o *^ S >- PAIRED FINS 79 (Goodrich [176]), and there is evidence that in Raja, for instance, theradial muscles of the pectoral fin retain the iDrimitive metamerism. We have now to account for the apparent migration of the if the ancestral Gnathostome had possessed continuous pairedfin-folds, the position of the paired limbs cannot be accounted forin phylogeny merely by their persistence in certain regions andsuppression in others. In all classes there has been perpetual. h(t- ss<j Fig. .02. Transverse section through the centre of A, a trunk vertebra of llaja. B, a caudal vertebraof Rhinahatus granulatus, Cuv. C, a tru7ik vertebra of Rhina squathia, L. D, left-side viewof a portion of the vertebral column, and of the skideton of the first dorsal tin oi Rhina squatina,L. bp, basal ; hi\ basiventral (haemal arch) ; c, centrum ; , calcareous ring ; , dorsal fin ;, haemal arch ; in, interdorsal; , V)asidorsal (neural arch) ; , neural canal; , neuralspine (or anterior radial); r, distal end of radial ; and , radiating calciflcation (black);sd, supradorsal. alteration of the position occupied by the paired limbs, just as inthe case of the unpaired fins of fish (Figs. 47, 51). It has beenheld (Gegenbaur) that these changes of position are due to the actualmigration of the paired limbs from one place to another. Nowembryology affords no evidence for this view. In ontogeny there islittle or no migration of
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