1889.] MR. W. K. PARKER ON STEATORNIS CARIPENSIS. 187 



5. Directly Desmognathous — In the majority of Families. 



6. Doubly Desmognatlious — Podargus, Steatornis, Bucerotidse 



(part). 



Of course the first three are varieties of the Schizognathous type, 

 as the last three are of the Desmognathous. 



The basipterygoids vary from complete abortion in the adult, 

 almost total suppression (in the Swift), to a very high state of deve- 

 lopment, almost Struthious, in Steatornis. They are large and far 

 forwards in the Trochilidse, and large in the middle region in the 

 Trogonidae. 



The endoskeletal post-palatine rudiment is just dying out m 

 the Caprimulgidae, and it is in Caprimulgus europoius that I have 

 found the greatest approach to Mgithognathism ; the large vomer 

 is formed from a pair of centres, but it is only united to the nasal 

 floor by ligament ; in the Swift the ^giihognathism and the post- 

 palatines are seen. 



The sternum takes on almost every possible modification in the 

 Coccygomorphse ; it may have an entire hind margin, as in the 

 Trochilidse and Cypselidse, or one or two pairs of notches. 



The interclavicle is almost as large as in the average Passerines, 

 or even in the Gallinacese, in Piuya cayana, Geococcyx affinis, 

 Coccyzus americamis, and Cuculus canorus ; it is present but small 

 in Saurothera vieilloti ; all these are true Cuculidse. 



In tlie Picida; and Alcedinidse and others the interclavicle is 

 suppressed ; in the Toucan, some of the Ilornbills {e. g. B. albiroa- 

 tris), and in Corythaix the rami do not unite; they do in many of the 

 Psittacidse, but the top, only, of each "ramus" remains in some 

 forms ; the top of the ramus is double, as in the Passerines, in Picus, 

 Hhamphastos, and Alcedo. 



The syrinx is extremely variable in this group, from its lowest 

 form in the Swift to a very high, but not the highest, in the Parrot. 

 In some of the Cuculidse the trachea is double a long way up, quite 

 hke what is found in the Chelonia (see Beddard. P. Z. S. 1885, 

 pp. 168-187). 



Nevertheless all these varying forms are, m some unknown way, 

 related, and related most intimately. You cannot cut up the group 

 without violence ; at their upper margin they interdigitate with the 

 great Passerine suborder ; any supposed near relationship of the 

 Coccygomorphse to any other type is, I believe, an illusion ; they 

 show in some cases a resemblance to the Owls, and in others, as in the 

 Musophagidse, to that most abortive and aberrant Curassow, the 

 Hoatzin (Opistkocomus) ; but I feel certain that in these cases there 

 is no true genetic affinity, it is merely adaptational isomorphism ; 

 or, in plain English, similar modification, in different types of birds, 

 to the same kind of life. 



The peculiarities of structure in Steatornis that are of most interest 

 are those that are shared by it with ancient and extinct Reptilian 

 types. Of course I do not forget that the whole of its organism is 

 in a certain sense Reptilian ; but although the bird grows up from 



