SKULL OF THE ^GITHOGNATHOFS BIRDS. 295 



Example 67. Skull of Swift {Cypselus apus), 1st summer. Family Cypselidae. 



Group Tracheophonse ^. 



Habitat. Great Britain. 



We saw that this particular form of palate was present in birds lying at a great 

 depth below the Passerine level ; there it was seen to be imperfect, although those birds 

 possess every element ; it is arrested in the metamorphosis in those birds, the Hemipods 

 {Turnix, Part I. pi. liv. Here, in the uppermost territory, in a small group, equal in 

 genera and species only to one of the smaller Passerine families, we have a most distinct 

 kind of bird with a perfectly ^githognathous palate. Therefore, if the morphology of 

 the face is to count for much in the classification of birds, I do not see how Professor 

 Huxley's " Cypselomorphse " (P. Z. S. April 11, 1867, p. 468) can be retained. I have 

 shown (Trans. Linn. Soc. ser. 2, Zool. vol. i. pp. 113-120) that two of the families placed 

 by him in that group are schizognathous, this simple reptilian condition of the palate 

 being retained by such high types as the Trochilidee and the Caprimulgidse. Feeling, as 

 I do, that classification may be left to take care of itself, if the facts of the organization 

 of the groups be made sure, I am not troubled to see that convenient little group break 

 itself up into three lesser groups, each of equal value. 



Although the border of the Swifts falls to them close on that " top-land " of the 

 Passerines where the Swallows congregate, yet are these conterminous groups only 

 " second cousins," and more alike in their habits and mode of dress than in their real 

 nature. I mentioned that those Swift-shaped Flycatchers, the Swallows, come up to 

 the true Sylviines in all that is normally Sylviine. Now a Swift, as to his skull and 

 face, is merely an exaggerated Swallow, an ultra-hinmdine bird — a caricature, as it 

 were, of the true Passerine gapiag birds. In the skeleton he comes close to the Hum- 

 ming-birds ; in the huge disproportion in length of the arm to the hand, even the 

 Swallow begins to be very Cypseline ; but the Swift and the Humming-bird are here at 

 one. So, also, are they in the sternum and shoulder-girdle ; the Swift also has lost the 

 " cseca coli," and has not developed any intrinsic muscles to the syrinx (' Shoulder-girdle 

 and Sternum,' plate xiii. p. 176 ; Macgillivray, Brit. Birds, vol. iii. pp. 606-626, pi. xxii. 

 fig. 5). These and many other characters that might be mentioned show that the Swift, 

 although claiming to have arisen from the same essential stock and root as its Passerine 

 relations, has, while failing to gain several of their most exquisite modifications, brought 

 that kind of framework for which even the Swallow is remarkable to its uttermost 

 degree of perfection ^. 



' The term " Tracheophonae " is applicable not only to those Coraoomorphae which have the syrinx imperfect, 

 but also to the remainder of the Carinatc birds. The title of these commimications, " On the ^githognathae," 

 gives me great liberty ; I am not bound to the Coracomorphfe, although they yield me nearly aU my materials ; 

 but I search everjTvhere for this particular form of facial modiiicatioB. 



' I think it is far from improbable that we owe that most exquisite creation, "Ariel," to the poet's familiarity 



