550 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



^Following the. description in Odontornithes Dr. Gadow" writes that 

 in Hesixn-ornis the clavicles articulate with the precoracoid process 

 onlv. Such a union can not be brought about in the specimen in the 

 Ignited States National Museum wiiil.% as said above, there is a very 

 evident union between clavicle and coracoid as shown in figure 4. 

 The importance of this is cn^dent, for if the clavicles ended in a point 

 and articulated only with tlie precoracoid the shoulder girdle would 

 have a strikinglv reptilian facies; as it is, the conditions are not very 

 unlike those found among existing birds. The retention of a complete 

 clavicle in a degenerate shoulder girdle is, however, an important 

 point, for in modern birds with degenerate wings it is the proximal 

 part of the clavicles which disappears, leaving the heavier distal por- 

 tion attached to the coracoids. The complete separation of the clavi- 

 cles and the fact that the proximal portion is much the heaviest is also 

 a generalized condition. 



The scapular arch of Hesperornis may be thus defined: Coracoid and 

 scapula free from one another, preserving all articular faces, and 

 forming little more than a right angle with one another; clavicles 

 complete, free, without scapular process, and articulating with the 

 coracoid. In struthious birds, on the other hand, the scapula and 

 coracoid are ankylosed in the adult, bear only the humeral articulation, 

 and form a very open angle with one another; clavicles absent or 

 vestigial and represented by distal ends only. 



In^skuU and shoulder girdle Hesperornis presents an interesting 

 combination of characters, on the one hand showing generalized fea- 

 tures and on the other close resemblances to modern birds. Thus we 

 have in the Cretaceous a bird with a palatal structure quite unlike that 

 of any struthious bird and with a vestigial wing which yet preserves 

 many features found in the liml)s of birds possessed of the power ol 

 flight. Add to this that no struthious l)ird is, as yet known, fron 

 North America,* and we ha^-e an argument for those who believe thai 

 if birds did not have a diphylletic origin they at least divided int( 

 two very distinct branches early in their career. 



In Animals of the Past attention was first called to the fact tha 

 the tarsi of Hesperornis were directed laterally outward almost a 

 right angles to the body, instead of being directed downward as ii| 

 other >)irds. This is brought about l)y the narrowness of the pelvij 

 and straightncss of the femur and ])y the outer and inner condyles o' 

 the femur being on the same level, instead of the outer being the lowe 

 of the two, as is usually the case among swimming birds. A simila 

 arningement, with similar results, is found in seals. From this poS' 

 tion of the tarsi it would seem that the legs should naturally have bee 

 moved together, like a pair of oars, instead of alternately, althoug 



"Newton's Dictionary of Birds, p. 858. 



^See that part of this paper relating to Diatryma. 



