162 STRUCTURAL AND SYSTEMATIC ZOOLOGY 



is larger in proportion to the face ; and the parts of the 

 brain are not situated in one plane, one behind the other. 

 The cerebrum is round and smooth, and the cerebellum 

 single-lobed. The ears resemble those of crocodiles ; but 

 the eyes are well developed, and protected by three lids. 

 They are placed on the sides of the head, and the pupil 

 is always round. The sexes generally differ greatly in 

 plumage, in some cases more widely than two, distinct 

 species, but the coloration of either sex of any one 

 species is very constant. 



There are two divisions of living birds. 



DIVISION A. Ratitae (jCursores) 



This small and singular group is characterized by 

 having no keel on the breastbone, rudimentary wings, 



feathers with discon- 

 nected barbs, and 

 stout legs. The Af- 

 rican ostrich has two 

 toes, the cassowary 

 three, and the apte- 

 ryx four. 



Its representatives 

 are the ostrich(5/r//- 

 thid) of Africa and 

 Arabia, South Amer- 

 ican ostrich (Rhea\ 

 cassowary ( Casua- 

 rins) of the East 

 Indian Archipelago 

 and Australia, emu 

 (Drom&us) of Aus- 

 tralia, and Apteryx, 



FIG. 140. African Ostrich (Struthio camelus). 



or kiwikiwi of 



Zealand. Besides these, there are extinct gigantic forms 



