412 STKUCTURE AND CLASSIFICATION OF BIEDS 



The lacrymal, as in Pelecamis and Fregata, is deeply notched 

 laterally. 



MiVAET, from his investigations into the axial skeleton 

 of this group/ set aside Phaeton and Fregata by reason of 

 their possessing twelve or thirteen cervical vertebrae and 

 the doubly notched (on each side) sternum of Phaeton, 

 besides a number of other points. 



There are seventeen cervical vertebra in Pelecanus, 

 eighteen in 8ula, twenty in Phalacrocorax. 



The atlas vertebra is notched for the reception of the 

 odontoid process in Pelecanus, perforated in Sula and Plotus ; 

 in Phalacrocorax the conditions are.intermediate, a perfora- 

 tion being only just closed above. 



The Steganopodes have catapophyses upon some of the 

 cervical vertebrae which enclose a canal ; in Pelecanus this 

 is found on vertebrae 8-15. In Sula the canal may com- 

 mence on the same vertebra, but more usually on the ninth, 

 extending to the thirteenth. In Phalacrocorax there are no 

 vertebrae with a complete haemal arch formed by union of 

 the catapophyses. In Plotus the canal begins on the ninth 

 vertebra and extends to the fourteenth. In Phaeton there is 

 no canal. The dorsal vertebrae are opisthocoelous in Phala- 

 crocorax and Plotus, not in Sula and Pelecanus. 



In all these genera the sternum is at most only slightly 

 notched by one notch only on each side. In Pelecanus the 

 clavicles are ankylosed to its keel. They reach it in Plotus, 

 Phalacrocorax., and Sula, but are only firmly connected by 

 ligaments, not ankylosed. In Phaeton the clavicles are 

 attached to the keel behind the extremity. 



Both spina externa and interna are wanting in Sula and 

 Pelecanus ; the spina externa is present, but small, in Phala- 

 crocorax ; contrary to the statement of Fubbeingbe (in 

 his tables) I find a rudimentary spina externa in Plotus 

 anhinga. Fregata and Phaeton show their divergence from 

 the normal steganopod type by a better developed spina 

 externa, while the latter bird may possess a rudimentary spina 

 interna. Four to six ribs reach the sternum. 



' ' On the Axial Skeleton of the Peleoanidte,' Tr. Z. S. x. p. 315. 



