AVES. RATITAE. 299 



Many ornithologists agree that the various forms grouped 

 together as Ratitae are not all very closely allied to one another, 

 that they resemble one another mainly in having lost the power 

 of flight, and do not form a natural group. 



The Ratitae include the following groups : 



JBpyomithes 1 , huge extinct birds from Madagascar. 



Apteryges, including the Apteryx of New Zealand. 



Dinornithes 2 , the Moas, huge extinct birds from New 

 Zealand, and some of the neighbouring islands. 



Megistanes, including the Cassowaries (Casuarius) of Aus- 

 tralia, New Guinea, and some of the neighbouring islands ; 

 and the Emeus (Dromaeus) of Australia. 



Rheornithes, including the Rheas of S. America. 



Struthiornithes, including the Ostriches (Struthio) now living 

 in Africa, and found fossil in N. India and Samos. 



Order 2. ODONTOLCAE. 



This order includes only an extinct N. American bird 

 ffesperornis 3 . The jaws are provided with a series of sharp 

 teeth placed in continuous grooves, but the premaxillae are 

 toothless, and were probably sheathed in a horny beak. The 

 rami of the mandible are not ankylosed together in front. 

 The skeleton is not pneumatic. The cervical vertebrae have 

 saddle-shaped articulating surfaces as in ordinary birds, and 

 the thoracic vertebrae are not ankylosed together. The tail 

 is comparatively long, and formed of twelve vertebrae with 

 only slight indications of a pygostyle. The ribs have uncinate 

 processes. The anterior limb is quite vestigial, being reduced 

 to a slender humerus. The posterior limb is very powerful 

 and adapted for swimming. 



1 See C. W. Andrews, P. Z. S., 1894, p. 108. 



2 See T. J. Parker, 2V. Zool. Soc. London, vol. xiti., pt. 2, 1895, and 

 F. W. Button, several papers in Tr. N. Zealand Inst., 1893 and 1895. 



3 See 0. C. Marsh. Odontornithes. A monograph of the extinct toothed 

 birds of N. America. Newhaven, 1880. 



