A treatise on zoology . The ceratotrichia are lost. Family Torpedinidae. In general structure the electric raysresemble the Ehinobatidae, but the tail is more distinctly marked off fromthe disk. The caudal fin is usually little developed, and the body issmooth. The disk is very rounded ; the median rostral cartilage hasbeen lost in Torpedo, but in Narcine a considerable rostrum edge of the disk is supported by the expanded pectorals, which donot nearly meet in front, the wide intervening space being filled bypaired rostral processes, and the greatly enlarged preorbital cartilagesar
A treatise on zoology . The ceratotrichia are lost. Family Torpedinidae. In general structure the electric raysresemble the Ehinobatidae, but the tail is more distinctly marked off fromthe disk. The caudal fin is usually little developed, and the body issmooth. The disk is very rounded ; the median rostral cartilage hasbeen lost in Torpedo, but in Narcine a considerable rostrum edge of the disk is supported by the expanded pectorals, which donot nearly meet in front, the wide intervening space being filled bypaired rostral processes, and the greatly enlarged preorbital cartilagesarticulating in front of the nasal capsules (Fig. 125). In Torpedo, i6: SELAC HI I while the hyoid copula has disappeared, the basal elements of thebranchial arches fuse to a single large plate. But the hypobrancliials aremore distinct than in the Rajidae. The ceratoh\-al is articulated to thehyomandibular {Torpedo), or to the first branchial arch {Hypnos). Thejaws become very slender and crescentic, and bear small Fig. 125. Ventral view of the skull and visceral arches of Torpetlo. (After Gej^eiibaur.) ao, enlargedaiitorbital process; b, fused basibratichials ; c, s[iii-aciilar cartilage; hm, hyomandibular;hy, hyoid arch : mJ:, Meckels cartilage ; , nasal cartilaj^e ; r, rostral process ; s, base ofcranium ; 1-4, first four branchial arches ; 5, fiftli branchial arch, -which abuts against thepectoral arch. The two halves of the pectoral girdle are not firmly fused ventrally,neither do they articulate as in the Rajidae with the vertebral column,but join above it to a median piece. The pelvic girdle has paired pre-pubic processes. The ribs are well developed. A large electric organ,supplied by a branch of the facial, and by four Ijranches of the vagusgroup of nerves, is situated between the branchial pouches and thepectoral fin, on each side of the head (Fig. 126). This organ, formed ofvertical prismatic columns of tissue, is probably a greatly enlarged and RAJIFORMES 1
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
