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XII. Notes on the Fins of Elasmohranchs, with Considerations on the Nature and 

 Homologues of Vertebrate Limbs. By St. George Mivabt, V.P.Z.S. 



Eeceived December 22nd, 1877. Read February 5tli, 1878. 



• [Plates LXXIV.-LXXIX.] 



In the following paper I describe certain fin-structures which I have not found to be 

 described elsewhere. 



Before proceeding to do so, however, I must express my grateful sense of the kindness 

 of my friend Dr. Gunther in placing at my disposal for examination and illustration 

 duplicate store-specimens of Elasmohranchs which I should otherwise have had no 

 means of investigating. The species referred to are Zygcena malleus, Mustelus antarc- 

 ticus, Notidanus cinereus, Scyllium canicula, Ginglymostoma cirratum, Chiloscyllium 

 ocellatum, Acanthias blainvillii, Spinax niger, Pristiophorus japonicus, Pristis cuspidata, 

 Rhynchobatus djeddensis, Trygonorhina fasciata, and Callorhynchus antarcticus. 



Besides these, I have made use, for comparison, of certain skeletons preserved in the 

 Museum of the Eoyal College of Surgeons, drawings of some of which have been made 

 through the kind permission of my friend Professor Flower and the other authorities 

 of that Institution. These are Lamna cornubica, Cestracion j)hilipj)i, Sguatina angelus, 

 Polyodon folium, and Polypterus bichir. 



It may be well first to describe the specimens examined, and then to make such 

 remarks as have suggested themselves in regard to Vertebrate limbs generally, and 

 the relations borne by the fins of fishes to the extremities of higher animalti. 



ZYG^NA MALLEUS. 



Dorsal Fin (Plate LXXIV. fig. 1). 



The dorsal fin in this species is sustained by a great number of very elongate and 

 closely set cartilaginous rays, or, as they may be for distinction termed, " radials." 

 which form three superimposed longitudinal series — one basal, one median, one distal. 

 The number of these radials bears, as far as I can perceive, no exact relation to the 

 number of subjacent vertebrae ; and the whole fin-skeleton is separated from the sub- 

 jacent axial skeleton by interposed fibrous membrane, the interval, however, being 

 less wide than half the depth of the shortest of the three superimposed series of 

 cartilages. 



The basal cartilages are twenty-six in number ; but the second and the eighth from the 

 preaxial end of the series bifurcate distally, and the last but one seems to be made 



VOL. X. — PART X. No. 1. — February 1st, 1879. So 



