THE VOYAGE OF THE ' CHALLENGER. ' 435 



related to the Cicomicta through Scopits, whilst the Falconidee are 

 probably, though much more remotely, connected with the Steganopods, 

 corresponds to the Ciconiiform.es of Grarrod *, with the addition, as he 

 had already himself suggested t, of the Tubinares. 



But his earlier definition of that group, in so far as it relates to the 

 absence in it of the accessory femoro-caudal muscle (B), will have to be 

 modified, inasmuch as this muscle is, as shown above, generally present 

 in the Tubinares. These, too, differ markedly from the other Ciconii- 

 formes in the well-developed pectoralis tertius (very small or absent in 

 the others), in the large size of the vomer, and the non-desmognathism 

 of the palate, though as regards this latter character it has already been 

 pointed out that the Albatrosses are nearly desmognathous, whilst the 

 desmognathism of the Cathartidae is of a different kind to that prevalent 

 in the other forms concerned. 



The two existing groups of Petrels are clearly related to each other so 

 much more nearly than to any other group of birds that it is evident 

 that they must have had a common ancestor that possessed the peculiar 

 features characterizing the Tubinares as an order. Such a form may 

 therefore be safely assumed to have had 



1. The characteristic nostrils of the group. 



2. The equally characteristic stomach and duodenum. 



3. Webbed feet, with a small hallux of a single phalanx. 



4. A double great pectoral muscle, and large pectoralis tertius. 



5. A formula AB.XY, a glutens primus, and an ambiens muscle. 



6. Short colic cseca of characteristic shape. 



7. A tufted oil-gland, and the pterylosis characteristic of the group. 



8. Aholorhinal schizognathous skull, with large depressed vomer, great 

 supraorbital glandular depressions, no basipterygoid facets, and a trun- 

 cated mandible. 



9. A short, broad, deeply-keeled sternum, more or less entire behind, 

 with strong clavicles. 



10. A peculiar humerus, and tibia with large cnemial crest. 



No living Petrel has this combination of characters ; the OceanitidaB z pl- Chall. 

 having lost their colic cseca, the Procellariidae the accessory semi-tendinosus pt. x j. p< Qi t 

 (T) muscle, and both groups having become specialized in other ways. 



Such an ancestral form as here indicated may be supposed to be an 

 early, and in some respects as shown by the large vomer, schizognathous 

 palate, large third pectoral muscle, and formula AB.XT more primitive 

 form, that diverged from the common stock of the Ciconiiform birds 



* Collected Papers, p. 218. 

 t Loc. tit. p. 521. 



2*2 



