FINS OF ELASMOBEAXCHS. 401 



seems to indicate that he is disposed to consider them to be derivatives from the axial 

 skeleton — as formed, perhaps, from modifications of diverging appendages of the ribs, 

 i. e. from rib-elements proceeding out laterally. He thus more or less returns, if I have 

 not misunderstood him, towards Goodsir's speculations. 



According to these various naturalists, the paired fins of fishes are derivations from 

 the axial skeleton or from the branchial arches, being of the nature of productions 

 ventrad or externad from such internal parts. Some of the authors cited regard the 

 skeleton of the limbs as essentially similar to that of the azygos fins. Such are Maclise, 

 Humphrey, Macalister, and (not certainly) Goodsir. 



Professors Owen and Gegenbaur, on the contrary, consider the paired and azygos 

 limbs as fundamentally difi'erent skeletal structures ; and Cuvier and Professor Huxley 

 also appear to have shared this view. I do not recollect to have heard or read nny 

 distinct statement by Professor Huxley on this subject; but in his 'Anatomy of 

 Vertebrates' ^ he speaks of " the interspinous cartilages or bones," of " the median 

 fins," as " as cartilaginous or osseous elements of the exoskeleton." 



The further fundamental distinctness between the paired limbs and the axial 

 (including the branchial) system appears to have been a view entertained by Cuvier 

 and also by Professor Huxley. I have myself distinctly enunciated the same view in 

 1870^; and later ^ I have declared my conviction "that the appendicular skeleton is no 

 mere portion of the axial skeleton, but a distinct system of parts appended to and more 

 or less closely and variously connected with the axial system." To this conviction 

 I now adhere more firmly than ever. 



As with the limbs, so also the azygos fins may be, and have been taken to be, either 

 parts of the axial skeleton, or parts fundamentally distinct therefrom. The third pos- 

 sibility that they may be partly axial and partly peripheral, is an opinion which I 

 believe has not been entertained hitherto by any one. 



The first view (that they are essentially axial) has been held by Geofli-oy St.-Hilaire * 

 and Maclise, probably by Professor Goodsir, and certainly by Professor Gegenbaur, 

 who tells us ^ that their skeletal supports, " erscheinen im einfachsten Zustande als 

 Gliedstiicke bedeutend ausgedehnter oberer Domfortsatzbildungen, die unter Ablosung 

 vom AVirbel zu grosserer Selbstandigkeit gelangen." 



The doctrine of the distinctness of these parts from the axial system appears to have 

 had the sanction of Cuvier; and it has been taught by both Professors Owen and 

 Huxley that the solid supports of the azygos fins were exoskeletal structures ; and this 

 view I have myself held and put forward ''. 



Altogether, then, the following views have been held : — 



' 1871, page 43. ■ ° Linnean Trans, vol. xxvii. p. 388. 



' Lessons in Elementary Anatomy, ] 873, p. 230. ■* Memoires du Museum, vol. ix. 1822, p. 89. 



^ Gnindriss d. vergl. Anat. p. 488. 



