1867.] PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. 467 



c. The second, third, and fourth toes turned forwards ; the first 



backwards. 



Alcedinidce. Meropidce. 



BucerotidcB. Momotidce, 



Upupid(Z. CoracidcE. 



d. The first and second toes permanently turned backwards ; the 



third and fourth forwards. 



TrogonidcB. 



This group, as I have already intimated, appears to occupy the 

 centre of the Desmognathous division — the Musophagidce approach- 

 ing the Aetomorphse, the Trogonidce the Cypselomorphee, and the 

 Alcedinidce the Pelargomorphee. 



It appears to me not improbable that it may hereafter be desirable 

 to divide this group into four, retaining the title of Coccygomorphse 

 for the second. 



• The Celeomorphje. 



ft 



The rostrum is straight and usually elongated, and there are no 

 basipterygoid processes. 



The maxillo-palatines are short lamellae, which, vphen longest, do 

 not extend beyond the outer edges of the palatines, and are sometimes 

 altogether rudimentary. 



The vomers are very delicate rod-like bones, which in some cases, 

 at any rate, remain permanently separate. 



The quadrate bone is remarkably short. 



The sternum has two notches on each side, posteriorly, and a forked 

 manubrial process. The carina extends to the summit of this pro- 

 cess, its anterior edge being little (or not at all) excavated. 



The clavicles have uo median process ; but their scapular ends are 

 expanded, as in the typical passerine birds. The scapula accessoria 

 has the same form as in the latter. 



The upper and posterior process of the tarso-metatarsus is tra- 

 versed by a number of canals (five in Picus) for the flexor tendons ; 

 and the outer distal head of the bone is divided into two parts, the 

 fourth toe, which is articulated with it, being turned backwards. 



In the second, third, and fourth toes the basal phalanx is shorter 

 than the penultimate. 



The tongue is long, slender, and protrusible ; and there is only one 

 carotid. 



The oil-gland is surmounted by a circlet of feathers. 



In this group I comprehend only the Picidce and Yungidce. 



It is very difficult to assign the Celeomorphse to their proper 

 place. Ordinarily they are associated together with the Psittaco- 

 morphse and Coccygomorphse in the * order ' Scansores ; but seve- 

 ral ornithologists liave pointed out the thoroughly vxnnatural cha- 

 racter of this assemblage; and it is more than thirty years since 



