THE PEDIGREE OF BIRDS 359 



of the keel on the breastbone presents no difficulty, for it 

 has disappeared in various " Carinate " birds, such as the 



has disappeared in various Carinate birds, such as the 

 burrowing parrot called Stringops. Of course the argument 



GLC 



Fio. 56. — Pectoral girdle and breastbone of an ostrich (Struthio). 

 sc, scapula; CO., coracoid ; PC, precoracoid ; f., foramen; OL.c, the 

 glenoid cavity with which the humerus articulates ; c.st.gr., the coraco- 

 sternal groove; ST., the sternum or breastbone, without a keel, but 

 convex outwards ; R., sternal portions of the ribs. From a specimen. 



is not conclusive. It is possible that the Tinamous are not 

 Ratitae, but very peculiar Carinatae which sprang from a 

 primitive stock with dromaeognathous palate and distant 

 affinities with the flightless Ratitae. 



