THE VOYAGE OF THE ' CHALLENGER.' 433 



V. THE AFFINITIES OF THE TUBINARES. 



The Tubinares as a group may be shortly defined as follows : 



Holorhiual 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 supraorbital 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 duode- 

 num ascending ; with a completely double great pectoral muscle, and a 

 well-developed pectoralis tertius ; with the femoro-caudal and semi-tendi- 

 nosus muscles always present, and the ambieiis and accessory femoro-caudal 

 only exceptionally absent. 



Some at least of these characters the structure of the hallux, the 

 formation of the nostrils*, 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 distin- 

 guish them from any other Avian order, whilst the combination 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 Zool. Chall. 

 closely connected with the Gulls (LaridaB), but the grounds for any such Ex p. vol. iv. 

 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 t, and differ widely from them in the important feature of 

 being schizorhinal +. 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 tertius of the 

 Petrels is altogether unrepresented in the Laridae. The character of the 

 caeca in the two groups is also quite different, and there are no special 

 osteological resemblances between the two groups so far as I can see, for 

 the mere schizognathous character of the palate is, we now know, not 

 necessarily a mark of affinity. The character of the young plumage, the 



* The Oaprimulgine genus Siphonorhis (Sclater, Proc. Zool.. Soc. 1861, p. 78) 

 perhaps approaches the Tubinares more nearly in this point than any other bird known 

 to me. 



t I cannot understand Professor Huxley's remark (Proc. Zool. Soo. 1867, p. 455) 

 that " the Gulls grade insensibly into the Procellariidse," 



\ Cf. Garrod, Coll. Papers, p. 128. 



