478 PROF. ST. GEORGE MIVAET ON THE 



metapterygium " extended upwards along the postaxial face of the mesopteiygium, 

 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 Ifotidanus 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 ^'arious cartilages like those of the anal of Notidanus (Plate LXXV. fig. 5), 

 or the pectoral oi Myliolates 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 Chimcera, which he interprets as having 

 a small proximal articular axial cartilage (answering to the mesopterygium oi Notidanus), 

 a large triangular cartilage distal to it and formed of preaxial rays coalesced, and a 

 metapterygium formed of coalesced postaxial rays. 



A comparison of Chimcera (or of Callorhynchus) with Scyllium shows, indeed, that 

 the metapterygia of the two are evidently homologous ; but a comparison of Chimcera 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 oi Notidanus — 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 Chimcera. 



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 [Murcena, Synibranchus, &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 



