1878.] PROF. M1VART ON THE FINS OF ELASMOBRANCHS. 117 



Hum canicula, Ginglymostoma cirratum, Chiloscy Ilium ocellutum, 

 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, Potyodon 

 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 coales- 

 cence 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 



