52 INVERTEBRATE ZOOLOGY. 



Class V. AvES Warm-blooded Vertebrates, showing 



many reptilian characters, but differing 

 from them in the possession of feathers. 

 These are epidermic structures closely 

 related to scales. The anterior limb is 

 modified to form a wing, generally giving 

 the animal the power of flight. Quad- 

 rate bone movably articulated with the 

 skull. A single occipital condyle. 



[Some have recommended the fusion of Reptilia and Aves into a single class, Sauropsida, 

 which is warranted not only on anatomical grounds, but by the possession of intermediate 

 fossil forms. It seems, however, more practical to retain them as separate classes, which if 

 we take living forms alone into consideration, is easy to do. The following fossil groups 

 may be given, preceding the living forms. They should have the value of Sub-classes: 



Sauruea Jaws containing teeth, tail elongated, containing 



a large number of vertebrae, with a pair of con- 

 tour feathers to each. Digits of the wing not 

 coalesced, three being armed with claws. 

 ' Archaeopteryx. 



Odontornithes Bird-like forms similar to recent birds, but with 



teeth in both jaws, inserted either in separate 

 alveoli, or in a common groove. There are two 

 groups of these birds, one having akeelless ster- 

 num allied to the Ratitae, the other with a keeled 

 sternum and allied to the Carinatae. 

 * Hesperornis^ Ichthyoniis.] 



Sub-class 1. Ratitae Breast bone flat. Clavicles not united to 



form a furcula. Feathers down-like or 

 plume-like. Running birds with small 

 or rudimentary wings. Cannot fly. 

 ■^ Struthio. 



Sub-class II. Carinatae Breast bone keeled. Furcula generally 



present. Contour feathers on wings and 

 tail. 



Order 1. Gallinacei Feet stout, for scratching. Hind toe on 



a higher level than the others. Edge of 

 upper beak shuts over lower beak. Sec- 

 ondary sexual characters common, in 

 form of combs, wattles, spurs, etc. 

 if Gallus, Perdix. 



