594 MANUAL OF ZOOLOGY. 



CHAPTER LXIV. 



DIVISIONS OF BIRDS. 



i. GENERAL DIVISIONS OF AVES. 2. CURSORES. 



OWING to the extreme compactness and homogeneity of the 

 entire class Aves, conditioned mainly by their adaptation to an 

 aerial mode of life, the subject of their classification has been 

 one of the greatest difficulties of the systematic zoologist. 



By Professor Huxley the birds are divided into the following 

 three orders : 



1. SAURUR^E. In this order the caudal vertebrae are nume- 

 rous, and there is no ploughshare -bone. The tail is longer 

 than the body, and the metacarpal bones are not anchylosed 

 together. This order includes only the single extinct bird the 

 Archceopteryx macrura, in which the long lizard-like tail is only 

 the most striking of several abnormalities. 



2. RATIT/E. This order comprises the Running birds, 

 which cannot .fly, such as the Ostriches, Emeus, and Casso- 

 waries. It is characterised by the fact that the sternum has 

 no median ridge or keel for the attachment of the great pec- 

 toral muscles. The sternum is therefore raft-like (from the 

 Lat. rates, a raft), hence the name of the order. 



3. CARINAT^:. This comprises all the living Flying birds, 

 and is characterised by the fact that the sternum is furnished 

 with a prominent median ridge or keel (carina); hence the 

 name of the order. The numerous subdivisions of this order 

 are mainly founded upon the structure of the palate. 



As regards the above primary divisions of Birds, there can 

 be no doubt as to their being very natural sections. A fourth 

 division, of equal rank, must now be added for the extinct 

 Odontornithes, and all four divisions may be best considered 

 as sub-classes, and not as mere orders* No difficulty, also, is 

 to be found in subdividing the Ratita, Saururce, and Odon- 

 tornithes ; but there is the greatest difficulty in establishing 

 natural subdivisions amongst the great sub-class of the Cari- 

 nattz, since this includes by far the greater number of known 

 birds. The classification of this group proposed by Professor 

 Huxley (like that of Mr Garrod), descending, as it does, to a 

 great number of secondary groups, is not only too compli- 



* If this view be taken, it will be advisable to give the name of Sauror- 

 nithcs to the sub-class, and to reserve the title of Saururce for the order. 



