290 VEIiTEDRATE ANIMALS. 



CHAl'TEK XXIX. 

 DIVISIONS OF B I E D S. 



Birds mny lie vaiiouslj' ilivided, but for our jjreseiit purpose it is 

 most convenient to regard them as divided into tlie following three 

 great primary divisions or suli-elasses : — 



1. IvATiT.E. — This division comprises the Running Birds, -nhich 

 cannut Hy, such as the <_)striclies, Kineus, and t.'assowaries. It is 

 chararteriseil liy the fact that the stcrjiuni has no median ridge or 

 keel for the attachment of the great |icctoral nuiscles. The stermmi 

 is therefore raft-like (Lat. i-iilrx, a raft), hence the name given to 

 this section. The liarlis of the feathers are separate. 



2. C'akinat.k. — This comprises all living Birds except the preced- 

 ing, and is characterised by the fact that tlie sternum i.'j furnished 

 with a prominent median ridge or keel (carind) ; hence tlie name 

 applied to the division. Under this head are inchi<led six smaller 

 divisions or orders. 



3. Odontohnitiies. — This sub -class comprises three orders of 

 fo.ssil Birds, the essential characteristic of which is that they pos- 

 sessed true teeth, siud-; in distinct sockets or grooves in the jaws. 



,Si;ji-CbASS I. RATIT^'E. 

 Order f'rRsor.ES. 



The Eunning or Cursorial Binls, comprising the Ostrich, Casso- 

 wary, Emeu, Ithea, and Apteryx, are characterised by the rndi- 

 lurntai-y condition of the wings, which ai'e useless as organs of Higlit, 

 and by the comjiensating length and strength of the legs. In ac- 

 cordance with this condition of the limbs, the bones have few air- 

 cells, and the lireast-bone is ilestitut(^ of the jirominent lidgc or keel 

 to which the givat muscles of the wings are attached (fig. 206, A). 

 Tlie twii sides of the ]ielvis are united together below in the (l.strieh, 

 anil in al] the pelvic aTch has great strength and stability. The legs 



