A treatise on zoology . ; 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 org
A treatise on zoology . ; 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 163 modified j^ortion of the visceral muscles, ;ind of totally diderent originfrom that of tlie Rajidae (Fritsch [141]). Tlie Torpedinidae appear to be much more closely allied to theRajidae than to the Centrobatoidei. Yet there is reason to believe thatthey should be derived independently from some Rhinobatid-like ancestor. Fio. 126. Torpedo with electric organ, , and brain exposed; view. On the right side onlythe .surface of the organ is exposed ; on the left the nerves which supply it are , branchial sacs ; GR, sensory canals of lateral-line system ; Lc, electric lobe of brain ; 0, eye ;!/V, trigeminal nerve ; K, vagus nerve. (After Gegenbaur, fi-om Sedgwicks Zoology.) (Jaekel). Of living genera Narcine is perhaps the primitive, andTorpedo one of the most specialised. Torpedo, Dum. ; Mediterranean, Atlantic, and Indian Ocean, to Eocene,Europe. Hypnos, Dum. ; Australian. Narcine, Henle ; troj^ical seas, andEocene, Italy. Astrope, M. and H. ; Indian Ocean. Temera, Gray ;Indian seas. Group C. Centrobatoidei. The rostral cartilage is usually lost, but the skeleton of the pec-toral fins grows forward to meet in front of the skull (Fig. 119, B). i64 SELACHIl The tail becomes very distinctly marked off, and slender; the singledorsal fin which alone remai
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