234 AVES. 



Siib-Class 2. Neornithes. 

 ORDER 1. RATIT^E. 



A study of the structure of the wing in the existing Ratite 

 (raft- breasted) birds, suggests that they are all descended from 

 families which once had the power of flight ; and there are 

 many reasons for believing that their ancestors were already 

 differentiated into several well-marked groups before the gradual 

 loss of functional wings commenced. These ancestors, however, 

 must have represented a lower grade in avian evolution than 

 the vast majority of existing Carinatae, as indicated by such 

 characters as those of the palate and quadrate bone. Ex- 

 cept in the highly modified Ostrich (Strathio), the vomer is 

 always broad behind, where interposed between the pterygoids, 

 palatines, and basisphenoidal rostrum. The basipterygoid pro- 

 cesses are large and functional. The proximal articular end 

 of the quadrate is undivided. The characters of the pectoral 

 arch seem to be the result of the degeneration of the wings. 

 The long axes of the fused scapula and coracoid are thus placed 

 approximately in the same line : the furcula is incomplete or 

 wanting; and the sternum is invariably destitute of all traces 

 of a keel. 



Sub-Order 1. Odontolcce. 



All the known Tertiary Ratites are running birds, not 

 adapted for swimming ; but one Upper Cretaceous family seems 

 to represent a less-specialized group of this order which must 

 have been of aquatic habits. These are primitive birds in 

 which (so far as the skeleton is concerned) Ratite characters 

 appear to predominate, though many close resemblances are 

 observed to certain modern Carinates, such as Colymbus. They 

 may, indeed, be regarded as an early specialized offshoot from 

 the common ancestral type of the two great surviving orders. 

 They are conveniently grouped together in a division named 

 ODONTOLC.E, in allusion to their possession of teeth in grooves. 

 Their vertebrae resemble those of modern birds, but the vomer ' 

 is perhaps more primitive than usual in that it is subdivided 

 into right and left halves in the only satisfactorily known genus. \ 



