302 STRUCTURE AND CLASSIFICATION OF BIRDS 



The Alectoropodes in this way : — 



1. Sternum with very deep inner notches (fig. 72, p. 128), 

 and with long costal processes, whose long axis corresponds 

 with the long axis of sternum. 



2. Hallux attached above the level of other toes. 



The former group, which undoubtedly, so far as the above 

 characters are concerned, is the more primitive, consists of 

 the curassows and the Megapodes, limited respectively to 

 Central and South America and to Australia and some of the 

 Indian islands. 



These two families are distinguished by Huxley mainly 

 on account of the differing form of the hallux ; but there 

 are other points of dissimilarity, not known at the time when 

 he wrote. The two families may be thus differentiated : — 



Cracidaa , Megapodidse 



1. Hind toe not so long in | Hind toe longer in pro- 



proportion to rest. ' portion. 



2. Oil gland feathered. ! Oil gland nude 



3. Biceps slip never 



present. 



Biceps slip sometimes 

 present. 



4. Two carotids. Left carotid only. 



5. Trachea generally coiled. I Trachea always straight, ' 



The Alectoropodes may be readily divided into three 

 groups, which may be thus differentiated : — 



The NuMiDiDiE. 



1. Second metacarpal without backward process. 



2. Costal processes outwardly inclined (thus forming 



a transition between Alectoropodes and Peris- 

 teropodes). 



The remaining families, which will be distinguished from 

 each other immediately, agree with each in differing from 

 the Numididae in both the points mentioned. 



Mbleagbid^. 



1. Postacetabulum longer than preacetabulum. 



2. Postacetabulum longer than broad. 



