338 AXXALS XEVr YORK ACADEMY OF SCIEXCES 



rived from Osteichtliyes of some sort, ir is liighlT probable that their 

 ancestors had fully developed nuchal, opercular and branchiostegal or 

 gular elements, and their disappearance may be accounted for by the 

 foregoing hypothesis. 



11). The "otic notch/' between the cornu of the tabulare and the 

 squamosal, \ras probably not a direct inheritance from rhipidistian con- 

 ditions but was progressively developed in the Stegocephali. 



12). From Watson's observations on Megalichthys it would appear that 

 the base of the skull was transmitted from the rhipidistian stem to the 

 earliest Stegocephali with very little change, but in the typical Stego- 

 cephali the median occipital condyle had been largely withdrawn and the 

 paired exoccipitals furnished the chief articular surfaces for the vertebral 

 column, while the interptervgoid vacuiiy, becoming much expanded, gave 

 rise to the well-known fenestrate palate with widely divergent pterygoids. 



CoMPAEATivE Study of the Peciobal Limbs ix Peiiniitive Fishes 



AXD TeTRAPODA 



ORIGIX A>a) EARLY HISTORY OF THE LOCOMOTIVE APPARaTES OF 



VERTEBRATES 



The problem of the origin of the Tetrapoda in practice is not easy to 

 circumscribe or isolate : for it is almost inextricably connected with other 

 phylogenetic and morphological problems, including some of the widest 

 scope. 



After we have compared the skulls of the earliest Tetrapods with those 

 of fishes and have adopted provisional views as to the homologies and 

 transformations of the various elements of the skull in the two classes, 

 we must take up the difficult prolilem of the origin of paired limbs of 

 cheiropterygial type from some form of piscine appendages. But no 

 satisfactory solution of this can he attained until the problem of the 

 origin of fins in general, including both median and paired fins, has been 

 attentively considered. Here we must weigh Gegenbaurs famous theory, 

 that the median and the paired fins have had a different mode of origin, 

 the paired fins being modified gill structures, against the opposing theory 

 that both median and paired fins have had a similar mode of origin, from 

 folds of skin: and after we realize the far-fetched and mystifying char- 

 acter of Gegenbaur's theory and the strength of the embryological and 

 palaeontological evidence in favor of the opposite theory that has been set 

 forth bv Wiedersheim (1892) and in more recent vears bv Goodrich, 

 Dean, E. C. Osbum (1906) and others, we come to the further realiza- 

 tion that paired limbs, paired fins and median fins are all purely acces- 



