;pO. 1320. 



NOTES ON FOSSIL BIRDS— LUCAS. 



549 



above its union with the coracoid in order to adapt itself to the curva- 

 (ture of the body. The suggestion may be made here that perhaps the 

 ankylosis of scapula and coracoid which occurs among struthious birds 

 may be of more value than is usually accoi'ded it. This ankylosis 

 occurs in these birds oidy, while the scapula and coracoid are in youno- 

 birds suturally united as in dinosaurs. 



The clavicle terminates distally in a small, slightly cup-shaped 

 expansion which articulates with a small facet on the head of the 

 coracoid. This is quite different from the description and figures in 

 the Odontornithes where the clavicles are represented as pointed 

 distally and articulating with the precoracoid process only, and 1 can 

 only suggest that the specimens examined by Professor Marsh were 

 slightly imperfect. 



Fi(i. 4.— Right clavicle and part op right coracoid op Hcsperornis rcgalis, natural size. The 



LINE SHOWS THE FACET FOR DISTAL END OF CLAVICLE. 



The proximal ends of the clavicles appear to have been only slightly 

 apposed, the major portion of the articulating surface l)eing directed 

 backward, proliably for union with the anterior end of the sternum. 

 We have in Harris's Cormorant a suggestion of how this condition of 

 things may have been brought about, for in this flightless bird the 

 keel of the sternum has aborted until its anterior end is even with 

 the anterior end of the l)ody of the sternum, and yet the keel still 

 supports the clavicles as in other cormorants. This is an extremely 

 good example of the retention of a morphological character while 

 the entire pectoral girdle is undergoing degeneration and has ceased 

 to be of use. 



The relations of the })ones of the pectoral arch in Hesperornis sug- 

 gest that the conditions of the sternum in cormorants, where the keel 

 IS confined to the anterior portion, vaay represent a primitive type of 

 sternum. Very similar conditions are found among the larger species 

 of pterodactyls where the bodv of the sternum is smooth but a large 

 anterior projection is present. 



