A treatise on zoology . iracle. is formed on its anterior face (Division 2). The movable eyelidsare lost. The tail becomes reduced in size, less heterocercal ; andthe dorsal fins shift backwards, even the first being always behindthe pelvic, on the tail. The trunk appears to spread outwards,chiefly owing to the enormous development of the pectoral not only may extend backwards so as to meet the pelvic 154 SELACHIl fins, but also grow forwards, passing above the branchial slits(Sqiiatinidae, Division 1). Further, the pectoral fins fuse with thesides of the head (Division 2), and may
A treatise on zoology . iracle. is formed on its anterior face (Division 2). The movable eyelidsare lost. The tail becomes reduced in size, less heterocercal ; andthe dorsal fins shift backwards, even the first being always behindthe pelvic, on the tail. The trunk appears to spread outwards,chiefly owing to the enormous development of the pectoral not only may extend backwards so as to meet the pelvic 154 SELACHIl fins, but also grow forwards, passing above the branchial slits(Sqiiatinidae, Division 1). Further, the pectoral fins fuse with thesides of the head (Division 2), and may grow forwards, below theeyes and above the mouth and nostrils, to meet in the middle lineat the front end of the rostrum. This remarkable development ofthe pectoial fins can be followed in the ontogeny of young skates(Fig. 117). By the coalescence of radials an anterior endoskeletalaxis is developed in the pectoral fin, similar to the original posterioraxis (Fig. 121) (Gegenbaur [153], Howes [219]). To support these B A. A, B, and C, tliree successive stages in the development of Torpedo ocellata, Raf. The externalgill-filainents have been removed on the left side, ap, anterior region of pectoral fin growingforward ; b, region of fore-brain ; ir, foiu-th branchial arch ; d, cloacal aperture; e, eye ; ,external gills ; , lower jaw ; n, opening of nasal sac; p, pectoral tin ; pv, pelvic fin; s, ridgealong which thepectoral fln will grow ; sp, spiracle ; , upper jaw ; y, stalk of , huge fins, the anterior vertebrae become fused into a continuoustube (Fig. 118), the pectoral girdle becomes firmly attached to itabove, by a specially differentiated suprascapula (Fig. 118), andgreatly strengthened and widened at the sides for the receptionof the basals. The lateral-line system becomes much modified,spreading over the expanded pectoral fins (Fig. 127). Theampullae, also, may be extended over their surface. A very definitearticulation, by means of two condyles, is es
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