326 VOYAGE OF H.M.S. CHALLENGER 



quintus. The peculiar form of the biceps brachii muscle, which is in two separate 

 parts, the humeral head forming a patagial slip. The presence of hsemapophyses on the 

 dorsal vertebrae, the centres of which are marked by more or less developed pneumatic 

 depressions. The non-pneumatic humerus. The different pterylosis, and the nearly 

 equal size of the lobes of the liver. The greater size of the hallux, which always has a 

 distinct nail externally (quite absent in Pelecanoides). 



" Pelecanoides stands alone (amongst the Procellariidse) in the absence of the ambiens 

 muscle ; the peculiar disposition of the femoral vein ; the absence of a hallux ; and the 

 single interclavicular air-cell. Moreover, as in Bulweria only of other Tubinares, 

 its myological formula is A.X., there being no accessory head to the femoro-caudal 

 muscle. 



" The Tubinares as a group may be shortly denned as follows : — 



" Holorhinal schizognathous birds with a large, broad, depressed, pointed vomer, and 

 truncated mandible ; with the anterior toes fully webbed, and the hallux either very small 

 and reduced to one phalanx, or absent; with a tufted oil-gland and large supra-orbital 

 glands furrowing the skull ; with the external nostrils produced into tubes, usually more 

 or less united together dorsally ; with an enormous glandular proventriculus and small 

 gizzard of unusual shape and position, and with the commencing duodenum ascending ; 

 with a completely double great pectoral muscle, and a well-developed pectoralis tertius ; 

 with the femoro-caudal and semi-tendinosus muscles always present, and the ambiens 

 and accessory femoro-caudal only exceptionally absent. 



" Some at least of these characters — the structure of the hallux, the formation of the 

 nostrils, 1 and the form of the stomach — are quite peculiar to the Tubinares, not being 

 found in any other birds, though of universal presence in these. These features alone 

 would at once suffice to distinguish them from any other Avian order, whilst the combina- 

 tion of other characters is as unique. It is therefore a difficult task to assign to this 

 group a satisfactory position in any arrangement of the class Aves, owing to its much 

 isolated position. 



" Most previous writers have considered the Petrels as more or less closely connected 

 with the Gulls (Laridse), but the grounds for any such collocation are very slight, in my 

 judgment, now that the structure of the two groups is better known. 



" The Gulls exhibit no trace of any of the characteristic peculiarities of the Petrels, 2 

 and differ widely from them in the important feature of being schizorhinal. 3 The peculiar 

 disposition in two quite separate layers of the great pectoral muscle in the Tubinares is 

 quite unlike anything seen in the Gulls or their allies, whilst the large pectoralis 



1 The Caprimulgine genus Siphonorhu (Selater, Proc. Zool. fioc. Lond., p. 78, 1861) perhaps approaches the 

 Tubinares more nearly in this point than any other bird known to me. 



8 I cannot understand Professor Huxley's remark (Proc. Zool. Soc. Lond., p. 455, 1867) that "the Gulls grade 

 insensibly into the Procellariidae." 



* Cf. Garrod, Proc. Zool. Soc. Lond., p. 37, 1878; Collected Papers, p. 128. 



