450 STRUCTURE AND CLASSIFICATION OF BIRDS 



complete for the same way in front of it. The division of 

 the trachea is carried upwards above the point where it is 

 externally divided into two tubes by an internal septum. 

 And in Aeipetes, though there is no external division of 

 the trachea, there is an incomplete internal septum. In 

 Diomedea, according to Swinhob, at any rate in two 

 species, the bronchi are long and convoluted, as in certain 

 storks. 



The petrels are schizognathous and holorhinal birds, 

 some with basipterygoid processes. The skull possesses a 

 small peculiar bone, which has been termed the ' ossiculum 

 lacrymo-palatinmn,' ' whose relations are sufficiently in- 

 dicated by its name. This bone occurs in many genera ; 

 but it is said to be of no great classificatory significance,^ 

 since it also occurs in birds so remote from the petrels and 

 from each other as Cuculidae, Cariama, and Laridse. The 

 skull is markedly excavate above the orbits for the supra- 

 orbital glands. The skull of an albatross {Diomedea melano- 

 phrys) is in more than one particular like that of the 

 steganopods. It is, it is true, schizognathous ; but the 

 interval separating the maxillo-palatines and the palatine 

 expansions of the maxillae in front of these is very slight ; 

 and, as Foebbs has observed, the downwardly curved 

 extremity of the vomer partly fills up this gap, though there 

 is no actual fusion between it and the maxillo-palatines. 

 The hooked bill is Fregata-like ; and the closely approxi' 

 mated and downwardly produced internal laminae of the 

 palatines are highly suggestive of the pelican. There are 

 always fifteen cervical vertehrce. The sternum varies so 

 much, from having a plain hinder contour to the presence of 

 two notches on each side, that its characters need not be 

 given in detail. 



The petrels can be divided into two families, the 

 Oceanitidae and the Procellariidse, which may be thus 

 defined : — 



' By Bbandi. Pabkek has termed it ' uncinate.' 

 ^ See, however, under Steganopodes, p. 416. 



