38 THE CLASSIFICATION OF BIRDS 



and mongrel group separating the aquincubital Pelargomorphaa 

 from the qnincubital .^Egithomorphae. There cannot be much 

 doubt that the fifth secondary was lost by the Pelargomorphas 

 very early in the history of the class. If not as completely de- 

 veloped as the other secondaries, it is always absolutely lost. No 

 instance is known of a rudimentary or vestigial fifth secondary. 

 That Dendrochelidon should have no trace of a fifth secondary, 

 whilst Cypselus has a fully developed one is a profound mystery. 

 I can offer no guess as to the possible explanation. 



The Coraciomorphae may be divided into four Orders, which 

 may be diagnosed as follows : 



CATHARTIFORMES. Coraciomorphae .in which the flexor per- 

 forans diyitorum leads to the first, second, and third digits ; the 

 fifth secondary is absent; the ambiens muscle is present; and 

 the nostrils are pervious. 



CORACIIFORMES. Coraciomorphaa in which the flexor perforans 

 diyitorum leads to all the digits, including the hallux ; the ambiens 

 muscle is absent ; and the nostrils are impervious. 



TROGO^IFORMF.S. Coraciomorphae in which the flexor perforans 

 diyitorum leads to the third and fourth digits only ; the second 

 digit is reversed ; and the nostrils are impervious. 



PlClFORMES. Coraciomorphae in which the flexor perforans 

 diyitorum leads to the third digit only; the fourth digit is re- 

 versed ; and the nostrils are impervious. 



CATHARTIFORMES. 



16. PSEUDOGRYPHI. 



The Pseudo- Vultures, the so-called New World Vultures, the 

 Pseudogryphi or Mimogypes, are very difficult to place in the 

 Systema Avium. It is agreed on all hands that they are not 

 Vultures, but whether they belong to the Falconiformes, the 

 Coraciiformes, the Ciconiiformes, or may reasonably claim to be 

 raised to Ordinal rank is an open question. I have adopted the 

 last-mentioned course on the ground that though probably nearest 

 related to the Coraciiformes, they differ so much from them that 

 they ought to be regarded as a distinct Order. 



The Cathartiformes, the Ciconiiformes, the Coraciiformes, and 

 the Falconiformes are all altrices. so that the condition of the 



