9o8 



STERNUM 



the MoAS (p. 579) shews that this feature may not be of more than 

 generic vahie. The little that is known of the sknll of GoMonm 

 suggests — though the suggestion depends perhaps chiefly on its 

 size — that it may have had some resemblance to that of the Phororha- 

 cidee, although of a more depressed form ; and the coracoid of Gast- 

 ornis is as elongated and narrow as that of Phororhacos. That the 

 Stereornithes were flightless may be considered certain, but whether 

 they should rank as a Subclass with the Puititai and Carinatx, or 

 should merely form an Order in one or other of these groups cannot 



Phoeorhacfs inflatus. Pelvis from the side and above. (After P. Ameghino.) 



as yet be determined, though the view taken by Dr. Gadow [Thier- 

 reich, Vogel, Syst. Th. pp. 106-114), who has placed the EurojDean 

 Bemiornis, Gastornis and Dasornis, together with the North- American, 

 Diatryma — all of them being Eocene forms — among the Stereornithes,^ 

 receives support from the evident connexion between the peculiar 

 and specialized Ungulates of South America and the Eocene Perisso- 

 dactyl Ungulates of the Old World and North America. 



ElCHARD LyDEKKER. 



STEBNUM, or Breastbone, that part of the Skeleton which 

 is connected with the vertebral column hy the thoracic ribs and 

 serves for the support of the CORACOIDS. Genetically it is wholly 

 of costal origin. In the chick, towards the end of the first week of 

 incubation (EiNiBRYOLOGY, p. 211), about 10 pairs of Ribs are con- 

 siderably elongated, so that their free ventral half extends forward 

 and approaches the middle line. The distal ends of each right and 

 left series soon meet and fuse, so as to form a " sternal band " of 



' This alliance was first suggested by the writer, who, in 1889 (Nicholson and 

 Lydekker, Man. Talxontol. ii. p. 1229), referred both Diait-ijma a,iid Mcsc)/ibrior7us 

 to the GastomitMdss. 



