44 PEOF. W. K. PAEKEE ON THE 



I had also made my own observations on the skeleton of an old male bird of this 

 species in the Hunterian Museum. Judging from the figures given by Prof. Huxley in 

 his second paper, I am of opinion that the specimens there figured were from skeletons 

 of female birds. 



What struck me at first in the Hunterian specimen was that it is much more like the 

 skeleton of a strong Curassow {Crax) than those from which Prof. Huxley's illus- 

 trations were taken ; these latter have a very Musophagine appearance ; they suggest 

 an evident relation to the Plaintain-Eaters. Thus, while I am glad to refer to those 

 figures, and the excellent descriptions given of them, and the accompanying remarks 

 on the affinities of this bird, my own notions of the structure of the adult, here given, 

 will be from observations on the Hunterian specimen. 



I. Introductory Bemarks on the Present Existence of Birds closely 



related to Beptiles. 



Two or three facts must be noticed at the outset of these remarks : namely, first, that 

 the known extinct forms are very few in proportion to the multitudes of those that are 

 still alive ; secondly, that the Teitiary forms are closely related to existing types, and 

 throw but little light on their origin ; and, thirdly, that the very few most ])recious 

 relics of the Secondary Kocks startle us at once by being tooth-bearers — not like our 

 familiar forms with their horny beaks. Leaving out of consideration the mysterious 

 and apparently quite isolated Arclioeojyteryx, the types described by Dr. Marsh in his 

 magnificent work on the " Odontornithes, or Extinct Toothed Birds of N. America," 

 1880, teach some very remarkable facts. If there is one modification of the skeleton 

 of a bird which, more than any other, is peculiar and typical, it is the mode in which the 

 presacral vertebrae, in the majority of cases, are articulated together; I refer to the 

 cylindroidal or heterocoelous condition of the centra. I lately showed (Proc. Roy. Soc. 

 1888, pp. 465-482) that a much greater number of modern or existing birds than was 

 hitherto supposed retain the old Eeptilian or Opisthocoelous condition in several of 

 their presacral vertebrae, namely, in the dorsal region ; and that this condition is seen 

 in arboreal Altrices, as well as in aquatic and semiaquatic Prsecoces. If that is not a 

 reptilian character I know of no one that can be described as such ; it is equal in value, 

 in my opinion, to anything that can be found in the skull, the shoulder-girdle, or in any 

 other part of the skeleton. 



Eor practical ornithological purposes the existing birds may be fenced off' into 

 two groups, namely, the Eatitae and the Carinatae. We thus get some two dozen 

 archaic forms, mostly from the Southern Hemisphere, and twelve thousand modern 

 forms with the Old World at their feet. Now all the existing Eatitae have their 

 presacral vertebrae cylindroidal ; whilst some of the most highly specialized and large- 



