REPORT ON THE ANATOMY OF THE PETRELS. 57 



The Literal position of the nostrils. 1 The presence of a distinct gluteus quintus 

 muscle. The formation of the biceps humeri muscle, which gives off a patagial slip 

 from its coracoidal head. The characteristic sternum. The absence of haemapophyses 

 on the dorsal vertebras. The pneumatic os humeri. The generally pneumatic condition 

 of the skeleton. The proportion of the manus to the humerus and ulna. 



The tongue and palate are also more or less peculiar, and in all the genera there are 

 uncinate bones, no basipterygoid facets, and two large distinct accessory wing-ossicles ; 

 the right liver-lobe is also distinctly the larger of the two. 



There are apparently three good genera of Albatrosses which may be distinguished, 

 independently of external characters, as follows : — 



Diomedea. Tongue very short ; uncinate bones more or less styliform. (Diomedea 

 exulans and brachyura.) 



Tludassiarche. Tongue intermediate ; uncinate bones styliform. {Thalassiarche 

 culminata.) 



Phabetn". Tongue much longer; uncinate bones flattened; hallux better developed 

 than in the other genera, and with an external claw. (Phoebetria fidiginosa ) 



Neglecting for the present the peculiar diving Peleeano'ides, the remainder of the 

 Procellariidae forms a natural group distinguished by the following characters from the 

 Albatrosses (Diomedeinaa) : — ■ 



The more or less dorsal position of the nostrils, the form of which however varies, as 

 has already been described, though they are never lateral. The absence of a gluteus 

 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 haemapophyses on the 

 dorsal vertebra?, the centre 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 Pelecanoldes.) 



Pelecanoides is, in some respects, as much specialised as the Albatrosses, though many 

 ■of its modifications are distinctly traceable to its diving habits, as, e.g., the compressed form 

 of the wing bones, the great development of the bypapophyses of the dorsal vertebrae, 

 the elongated sternum and pectoral muscles, the peculiar ribs. But it stands alone 

 (amongst the Procellariidae) in the absence of the ambiens muscle ; the peculiar disposi- 

 tion 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. 



1 This feature, in which the Albatrosses are apparently more primitive than are either the Oceamtitlcc or the other 

 Procellariidae, can hardly, if my views about the relationships of these groups to each other be correct, be considered to 

 have been a character of the common Petrel-ancestor. It may be more probably explained as due to arrested develop- 

 ment during embryonic life, as a study of the development of the nostrils of other Petrels would probably show that 

 these are actually, at some time, lateral, anil subsequently coalesce 



(ZOOL. CHALL. EXP\ PART XI. —1882.) L 8 



