OEGANIZATION OF THE OKNITHOSAUEIA. 85 



The form of the cerebellum, tlie size and position of the cere- 

 bral hemispheres, and the inferior and lateral place of the optic 

 lobes in the skulls of Pterodactyles offer another coincidence 

 of distinctive structures with those of the class Aves. These 

 are the only vital organs of birds which have a palseontological 

 value : with them may be associated any bones that the condi- 

 tions of existence tend to elaborate. Any corresponding concep- 

 tion of a reptile is unattainable ; hence ideas of the boundai'ies of 

 the Eeptilia must always be vague. 



Professor Huxley, in 1867*, so far modified the ordinary con- 

 ception of a reptile as to maintain that the Ornithosauria were 

 reptiles with hot blood. I had previously t detailed reasons for 

 believing that they were hot-blooded, but had inferred for them 

 from that an affinity with birds. It is within the limits of possi- 

 bility for a reptile to be hot-blooded without having the organs 

 associated with hot blood in mammals and birds, since there are 

 hot-blooded fishes. 



Professor Huxley followed up his belief that Ornithosaurs were 

 hot-blooded reptiles by another belief that the pneumaticity of 

 the bones and the avian characters of Ornithosaurs might be 

 merely adaptive modifications X- By that expression Professor 

 Huxley evidently intends to convey the impression that the struc- 

 tures in question are resemblances consequent upon the parts of 

 the body having had to perform identical functions, so that the 

 bones of different animals have acquired identical shapes and 

 structures. Por he goes on to say, " Pterodactyles, among rep- 

 tiles, approach birds much as bats among mammals may be said 

 to do. They are a sort of reptilian bat rather than links between 

 reptiles and birds ; and it is precisely in those organs — the manus 

 and the pes — which in birds are the most characteristically 

 ornithic, that they depart most widely from the ornithic type "J. 

 I have given reasons for thinking neither manus nor pes the 

 most characteristic organs of birds, and believe that brain and lungs 

 are organs of incomparably greater value in questions of organiza- 

 tion. When, therefore, Professor Huxley launches this scientific 

 dictum without facts to support it, we may usefully compare his 

 views as given at the Zoological Society. " Birds," says Professor 

 Huxley, " have hot blood, a muscular valve in the right ventricle, 



* " Classification of Birds," P. Z. S., 1867 p. 417. 



t Ann. Nat. Hist. 1866. 



I Popular Science Review, 1868, p. 242, being a, Royal-Institution lecture. ' 



