548 PROCEEDINGS OF THE NATIONAL MUSEUM. ^l. xxvi. 



unlike the condition prevailing- among the Dromfeognathfe, in which 

 there is an extensive interorbital ossification. 



Not only the component bones of the lower jaw, but the majority' of 

 those included in the cranium, appear to have l)een free from one 

 another, with the exception of the premaxilla?. Whether this is due to 

 the age of the individual or is a character common to the members 

 of the genus Hesperornis can not now be decided; nor is it certain 

 whether or not this freedom extended to the bones of the ])rain case, 

 as the skull of Hesperornis gracilis has this portion still embedded in 

 the mati-ix. In the Yale specimens the bones of the brain case appear 

 to have been fused, although it is said that man}^ of the other bones 

 were free. 



The example of Hesperm^nis regalis in the United States National 

 Museum lacks the calvarium, but the bones of- the jaw are quite free 

 and so are two supposed to be the lachrymal and nasal, the former of 

 which is here figured. 



SHOULDER GIRDLE OF HESPERORNIS REGALIS. 



Turning to the shoulder girdle, my own interpretation of this portion 

 of the skeleton, based on material in the United States National Museum,'^ 

 differs somewhat from that given by Professor Marsh in the memoir 

 on the Odontornithes, the most important points being the shape of 

 the distal end of the clavicle and the fact that the scapula and cora- 

 coid do not lie practically in the same plane, but the angle formed by 

 them is little more than a right angle, which is different from what 

 is found among struthious birds. That the scapula and coracoid are 

 quite free from one another and posvsess all the articular faces found 

 in corresponding bones of birds of flight is, of course, well known. 



While the open angle between the scapula and coracoid of struthious 

 birds was used by Huxley as one of the diagnostic characters of the 

 Ratitiv, it has come to be quite generally regarded as mereh' due to 

 degeneration, and practically a qviestion of mechanics; as the coracoid 

 shortened the proximal end of the scapula would be lowered and the 

 coraco-scapular angle opened, until with a greatly abbreviated coracoid 

 the scapula was almost in line with it, as in Casuarius. That the coraco- 

 scapular angle in Hesperornis, a bird with a vestigial wing, is less open 

 than in the Dromteognatha? is perhaps still a question of mechanics. 

 The struthious bii-ds are heavy, s^hort-bodied land birds, whereas Hes- 

 perornis was a long, lithe, proportionately slender-bodied diver, and 

 unless the entire scapular arch was reduced the scapula could not be 

 turned upward sufficientl}' to form an open angle with the coracoid. 

 In this connection it may be noted that in Rhea, which has a rather 

 long coracoid, the scapula is bent abruptly downward a short distance 



"This speciiiien comes from the gray chalk, and the bones are but little crushed or 

 distorted by pressure. 



