J. K. ThacJier — Median and Paired Fins. 297 



Most of the inoditications introduced by Huxley, though perhaps 

 not all, spring from a question which is independent of any theory 

 with regard to the skeleton, archipterygium or other, but which, 

 superior to them, must determine the application of them to the 

 passage fi-om the tisli limb to that of Stapedifera. 



If an Elasmobranch pectoral fin, for example, of Mustelus, be re- 

 moved and laid on the corresponding hand, with the propterygial edge 

 toward the thumb, and the metapterygial edge toward the little 

 linger, then the ventral surface of the fin will look in tlie same direc- 

 tion as the palmar surface of the hand. But if it be turned over so 

 that the metapterygial edge corresponds to the thumb and the prop- 

 terygial to the little finger, then the dorsal surface of the fin will 

 correspond to the palmar surface of the hand. 



One or the other of these views must be taken. There is no third 

 possible. Huxley takes the first, Gegenbaur the second. This, how- 

 ever is no new question and no new difference of opinion. Cuvier, 

 following Bakker, named the two ossifications of the scapulo-coracoid 

 which are so generally found in osseous fishes, radius and ulna. 

 Owen simply reversed this nomenclature and Mettenheimer followed 

 him. The question was the same as now respecting the homologies 

 of faces and edges of fin and limb. On the one side, then, we have 

 Bakker, Cuvier and Huxley ; on the other, Owen, Mettenheimer and 

 Gegenbaur. The weight of evidence seems to me to be in favor of 

 the view entertained by the latter group, namely, that the metaptery- 

 gial edge of the fish fin corresponds with the radial or thumb side of 

 the hand, and consequently that the dorsal surface of the fish fin is 

 the palmar (or plantar) surface. But I have no new facts. 



By reviewing Gegenbaur's work it will be seen that this theory of 

 his rests upon the form of the limbs in the Elasmobranchii and 

 Dipnoi. In the former grouj) it is the hind limbs which furnish 

 nearly all the evidence. The fore limbs (pectorals) are brought in 

 merely to testify to the hiserial character of the archipterygium, of 

 which no Elasmobranch ventral gives a sign. That is to say, the ven- 

 trals having testified to the archipterygium, and that having been 

 accepted, the pectorals find use for themselves in showing thai it 

 was fringed down tlie median as well as the lateral side. If then the 

 same form of limb is found in Elasmobranch and Dipnoan, the same 

 form was undoubtedly possessed by their common ancestors. But as 

 their common ancestors were also undoubtedly common ancestors of 

 all Gnathostomes, therefore all Gnathostome limbs must have been 

 derived from this form. 



Trans. Conn. Acad., Vol. III. 38 February, 1877. 



