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Show 1878.] PROF. MIVART ON THE FINS OF ELASMOBRANCHS. 117 Hum canicula, . Ginglymostoma cirratum, ChiloscyIlium ocellatum, Acanthias blainvillei, Spinax niger, Pristiophorus japonicus, Pristis cuspidatus, Rhynchobates djeddensis, Trygonorhina fasciata, and Callorhynchus antarcticus; and I add notes made from preparations of Lamna cornubica, Cestracion phillippi, Squatina angelus, Polyodon foliosus, and Polypterus bichir. Besides wishing to ascertain the positive conditions of skeletal structures in these forms, the examinations were partly undertaken with a view to the questions:-• (1) What is the nature of Vertebrate limbs generally ? (2) What is the relation of Piscine to other limbs ? To these questions four others are subordinate :- A. Are the paired-limb structures of a nature distinct from that of azygos fins ? B. Are paired limbs essentially axial structures which have become more or less detached from skeletal axis, or peripheral structures which have become secondarily more or less connected with it? C. What is the nature of limb-girdles ? D. What is the line of genesis of the cheiropterygium. I then note and discuss the opinions on these matters of Oken, Carus, Cuvier, Owen, Maclise, Goodsir, Humphrey, Gegenbaur, Macalister, Huxley, Balfour, and Parker. I have myself arrived at the conclusion that the nature of the paired and azygos limbs is fundamentally the same. I have, in fact, been brought to this conviction by finding various degrees of coalescence between the cartilaginous rays supporting the dorsal fins, and various degrees of connexion or continuity between such fin-supports and the subjacent axial skeleton. I have noted coalescence amongst the rays in Scyllium canicula, Ginglymostoma cirratum, and especially in Notidanus cinereus, where it is carried to such an extent that the rays are supported by one continuous basal cartilage. Continuity with the axial skeleton is described as existing in the dorsal fin-cartilages in several forms, but especially in Pristis and Pristiophorus; and I would suggest that the lateral pressure of its saw-like rostrum must be more or less aided by very firm fixation to the vertebral column of the cartilages supporting the dorsal fin. I have found much resemblance between the skeleton of the ventral and the dorsal fins, as, for example, in Notidanus, in Chiloscyllium and Raia ; also between the anal and ventral fins, as again in Notidanus. But the ventral fin of Polyodon is the most striking, presenting as it does a longitudinal double series of simple parallel rays, quite like the simplest form of the skeleton of the dorsal fins. Now, as the ventral and pectoral fins are admitted on all hands to be of the same nature, if the ventrals are of the same nature with the azygos fins, the pectoral ones must be also of that same nature. As to the objection which may be drawn from the attachment of the pectoral fins to the axial skeleton by a shoulder-girdle instead of by a direct continuous longitudinal adhesion, as in some dorsal fins, I observe:-(1) The pectoral-fin support could not continuously adhere to the axial skeleton longitudinally without impeding the flexure of |