184 MR. yf. K. PARKER ON STEATORNIS CARIPENSIS. [Apr. 2, 



are only present in birds that have arrived at the highest state of 

 ornithic modification and perfection. 



In the self-same skull we have then, as I hare shown, a basis 

 cranii with large backwardly placed " basi-pterygoids " that are 

 nearly Struthious ; the only carinate bird that is a rival to Steatornis 

 in this respect is Pallas's Sand-Grouse (Syrrhaptes paradoxus) (see 

 Trans. Zool. Soc. vol. v. pi. xxxvi.). 



On the other hand, the "ethmo-nasal wall" has been com- 

 pletely broken through and thus a complete hinge of the face on the 

 skull has been formed exactly as in the Parrots, where the mobility 

 of the upper face is at its greatest possible perfection. But the 

 basis cranii of the Parrots, in harmony with the " palato-quadrate " 

 arcade, is in the highest state of modification ; no bird is so far from 

 the old quasi-reptilian Ratitae in this respect as the Parrot. 



Yet, as a set-off against this, whilst the Archaic Ratitae have all 

 their pre-sacral vertebrae in the highest ornithic perfection, namely, 

 cylindroidal, in the Parrots the dorsals are opisthocoelian ; so they are 

 as we have seen in Steatornis, which also has the rare condition, as 

 in Eesperornis and the Grebes, of perfect rib-bars on the axis '. 



In Wading and Water Birds this state of things is common, e.g. 

 in the Penguins, ^/ciwe Divers^ Gulls, and LimicolcE ; but the Psit- 

 tacidse and Steatomis are the only high-class arboreal birds in which 

 I have found this character of opisthocoelous dorsals. 



Here I may remark upon a most puzzling fact with regard to both 

 old and new kinds of birds, namely, a prolepsis, or anticipation, so 

 to speak, of Mammalian characters, in certRin birds — a similarity or 

 isomorphism rather, for here "genetic aflBnity" has no place. 



The more Archaic the type of any one of the existing Ratitae, the 

 more complex is the nasal labyrinth, quite similar in its complex 

 "outgrowths" to what we see in a mammal. The very dorsal 

 vertebrae that are ancient or opisthocoelian in a Parrot, are also 

 like the vertebrae of a Mammal — they have thin terminal epiphyses. 



In by far the noblest of all birds, the Crows and Songsters, the 

 form of palate which gives them their morphological name, " ^gi- 

 thognathsp," is quite similar to what is seen in the Marsupials and 

 low Insectivorous Mammals. 



In this very bird, Steatomis — as in Podargus, the larger Bucerotidae, 

 and in certain Ducks and Swans — there is a degree of double Besmo- 

 gnathism quite similar to that which exists in the Marsupialia. 



Hence we had better, at present, speak of these things as cases of 

 isomorphism, or similarity — confessing our ignorance of their 

 meaning — than rashly to set them down to genetic relationship. 



By taking this character or that, and closing the eves to the other 

 characters seen in Steatomis, we might find many a relation for it : 

 it is, nevertheless, a friendless bird, I cannot find a near relation 

 for it. And this is the more evident if we consider that the forms 

 that apparently come nearest to it are Eastern and Australian types, 



^ In typical Chenomorphae — Grecse, Swan, Ducks — the atlas, also, has its 

 rib-bar complete, and a separately ossified rib. 

 ' Isot in the Loons and Grebes. 



