472 PROF. ST. GEORGE MIVART ON THE 
the ventral azygos fin-fold. The peculiar and apparently essentially axial nature of the 
solid supports of the ventral part of the caudal fin seems to tell against this hypo- 
thesis; but it need not necessarily do so, since, if we may suppose these subcaudal 
ingrowths in certain forms to have taken place very early, they would have acquired an 
integration with the skeletal axis much surpassing that of their dorsal homotypes, with 
a resulting difference of development and appearance such as we find now in the caudal 
structures here noticed. 
But the caudal fins of different kinds of fishes may have arisen in different ways in 
different cases, and apparent superficial resemblances may be due to the action of homo- 
plasy. The ventral portion of the caudal fin of Murena, that of most Teleosteans, and 
that of Elasmobranchs may have been derived independently from the primeval caudal 
ieee 
It remains to consider the relations existing between the paired fins of fishes and the 
limbs of higher Vertebrates, and also the development of the cheiropterygium. 
Before entering upon detailed comparisons, it must first be determined which part 
of the pectoral fin is preaxial and homologous with the radial side of the arm and 
hand? 
As to the first question, I think there can be no doubt that the view entertained by 
Cuvier and Huxley is the right one, and that the preaxial margin of the pectoral fin is 
that margin which is turned obliquely dorsad. 
To this view Professor Gegenbaur, though at first opposed to it, has now adhered ? 
as the more probable; and I marvel that Mr. Thacher still prefers the opposite one %. 
I marvel all the more because his own paper seems to me to be by itself capable of 
demonstrating the truth of the view which he is disposed to reject; for it shows 4 (as 
was long ago shown by Swan”) that the more preaxial spinal nerves go to the dorsad 
or propterygial side of the fin, while the more postaxial spinal nerves go to the ventrad 
or metapterygial side of the fin. 
If, then, the view here advocated is correct, 7. e. if the true pectoral archipterygium 
had a skeleton like that of the first dorsal fin of Chiloscyllium, the second dorsal of 
‘ Since this paper was written, Mr. Alexander Agassiz has very kindly sent me a paper of his (from the 13th 
vol. of the ‘ Proceedings ’ of the American Academy of Arts and Sciences) on the development of the tail in some 
species of fishes. In this very interesting memoir the frequent absence of vertical homology between the parts 
respectively on the ventral and dorsal sides of the upturned extremity is made very evident, the ventral portion 
being a secondary growth in the Flounder, and in Atherina, Batrachus, Lumpus, Ctenolabrus, Poronotus, 
Lophius, and Gasterosteus. 
? Morpholog. Jahrbuch, 2nd. yol. 3rd Heft, ‘‘ Zur Morphologie der Gliedmassen der Wirbelthiere,” p. 396. 
5 He says, ‘“‘ The weight of evidence seems to me in fayour of the view .... . that the metapterygial 
edge of the fish-fin corresponds with the radial or thumb-side of the hand.” 
+ In a section on “ The Innervation of the varied Fins in Mustelus canis” (1. ¢. p. 304). 
5 See Swan’s “ Illustrations of the Comparative Anatomy of the Nervous System,” 1864, p. 32, plate xi. 
