478 PROF. ST. GEORGE MIVART ON THE 
metapterygium ‘‘ extended upwards along the postaxial face of the mesopterygium, 
until it has not only reached the articular surface of the pectoral arch, but furnishes a 
large part of the articular cavity. In like manner the proximal preaxial ray (proptery- 
gium) has ascended along the preaxial face of the axial cartilage,until it also is able 
to furnish a facet which completes the anterior part of the cup for the condyle of the 
pectoral arch.” 
But even in Notidanus both the pro- and the metapterygium contribute to form the 
articular cavity; it is no wonder, therefore, that they do so in Scyllium. 
The Professor then goes on to speak of Squatina and Raia, treating them as steps 
further and further removed from the archipterygium. But these structures are at 
least as explicable on the other (as I believe, correct) view, namely that they are more 
and more near to the archipterygium. 
Evidently, on the centripetal theory, the rays incipiently coalescing proximad would 
first form various cartilages like those of the anal of Notidanus (Plate LX XV, fig. 5), 
or the pectoral of Myliobates aquila (Gegenbaur, plate ix. fig. 14), before coalescing 
into three cartilages, viz. into the pro-, meso-, and metapterygia. 
He then proceeds to consider the pectoral of Chimera, which he interprets as having 
a small proximal articular axial cartilage (answering to the mesopterygium of Votidanus), 
a large triangular cartilage distal to it and formed of preaxial rays coalesced, and a 
metapterygium formed of coalesced postaxial rays. 
A comparison of Chimera (or of Callorhynchus) with Scyllium shows, indeed, that 
the metapterygia of the two are evidently homologous ; but a comparison of Chimera or 
Callorhynchus with Notidanus can, I think, render it as little doubtful that Professor 
Huxley’s axial cartilage, instead of being mesopterygial, is the homologue of the pro- 
pterygium of Votidanus—as Gegenbaur has determined it to be. The triangular carti- 
lage distally united to the propterygium is also, I think, manifestly propterygial. In 
this case the mesopterygium has disappeared altogether as a distinct part; but in 
Scyllium it is much reduced—so much so that a slightly greater reduction would give 
the condition which we find in Chimera. 
This comparison strengthens the view that it is the mesopterygium which is absent 
in Chiloscyllium ocellatum. 
I regard the Rays as showing pectorals more approaching the true archipterygium 
than those of other Elasmobranchs. 
It is, I think, evident that there is a tendency to an inverse development between 
the lateral and azygous folds and their derivatives. In fishes in which the paired fins 
are minute or absent (Murena, Symbranchus, &c.) the azygos fins are extensively 
developed ; and when, as in the Rays, the paired fins are in excess, the azygos fins tend 
to disappear. On this account, if on no other, we should, I think, regard the Ray 
form of dorsal fin-skeleton as less primitive than the simpler form of Sharks. 
By analogy the simple, multiradiate, paired limb-skeleton of the Rays seems to point 
