xm 



PHYLUM CHORDATA 



413 



more or less deep notches (A, B) or foramina (G). In the Ratitae 

 (E) the keel is either absent or reduced to the merest vestige, and 

 there is no trace of the carinal ossification in the young. External to 

 the coracoid grooves the anterior edge of the sternum is produced into 

 larger or smaller antero-lateral processes (ant. lat. pr.) ; in the Emu 

 these are of great size and are closely applied to the pericardium. 



It was upon the characters of the raft-like sternum that the 

 group Ratitae was 

 founded, but the 

 difference between 

 them and the 

 Carinata) in this 

 respect is not ab- 

 solute, the ratite 

 condition having 

 been acquired by 

 many Carinatse 

 which have lost 

 the power of flight. 

 The keel is very 

 small in Ocydro- 

 mus, Notornis, and 

 Aptornis, three 

 flightless Rails 

 the last extinct 

 from New Zea- 

 land, and is prac- 

 tically absent in 

 the Dodo (Didus) 

 and Solitaire 

 (Pezophaps), two 

 gigantic extinct 

 Pigeons from 

 Mauritius and 

 Rodriguez, in the 

 Kakapo or 

 Ground-parrot 

 (Stringops) of New 

 Zealand, in the extinct Giant-Goose (Cnemiornis) from the same 

 country, and in Hesperornis. The absence of the carina may 

 therefore be considered as an adaptive modification of no significance 

 as indicating affinity. 



The entire order of Penguins (Impennes) and the extinct Great 

 Auk (Alca impennis) are also flightless, but their wings, instead of 

 being functionless, are modified into powerful swimming paddles 

 (Fig. 1074). There has therefore, in these cases, been no reduction 

 either of the pectoral muscles or of the carina. 



FIG. 1074. Eudyptes pachyrbynchus (Penguin). Skeleton. 

 (From a photograph by A. Hamilton.) 



