1867.] PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. 421 



4. The prefrontal processes are little ossi6ed. 



5. The bodies of the proper sacral vertebrae do not unite with the 

 pubes or ischia ; and the centra of the sacral vertebrae, which ossify 

 late, are extremely elongated and slender. 



6. The short sternum narrows posteriorly, and presents a notch in 

 the middle of its posterior edge. 



7. The length of the humerus exceeds the distance between the 

 shoulder-girdle and the ilium, and is of course greatly longer than 

 the scapula. The manus has the same conformation as that of 

 Strut hio. 



Fig. 2. 



Under view of the skull of Rhea avwricana. 



Pma\ The prajmaxillre. i?. The rostrum, ^/.i^j. Themaxillo-palatine. Jo. The 

 vomer. PL The palatine. Ft. The pterygoid. * The basipterygoid pro- 

 cess of the sphenoid. 



