

AND AVES OF NORTH AMERICA. 



51 





the others more oval, the move anterior arc sub-triangular, and the rib pits on the first dorsals are sub-round or 

 vertically oval. Tims the heads of the ribs also vary. The shafts are all Hat, probably more so from pressure. They 

 arc frequently curved in the direction of the compression, which suggests a vertical head. They however are probably 

 more or loss distorted, and the plane of compression changed. No well defined distal extremity of a rib can be made 

 out, nor have anything like abdominal ribs been preserved. 



The scapular arch is remarkable for its large clavicles (or proooraooids). As preserved, the latter are quite con- 

 vex downwards both, antero-posteriorly and transversely, while the eoracoids are equally concave in both directions. 



Fig. 7. 



Scapular Arch. 



The clavicles have a remarkable external Mai projection, which is separate,! from the glenoid cavity by a deep sinus. 



The gl( i,| cavity is bounded by an elevated ridge, which sends a, branch along the clavieulo-eoraeoid suture to the 



precoracoid foramen. This foramen is relatively of small size, and is a longitudinal oval ; the two arc separated by 

 an isthmus composed equally of processes of clavicle and coracoid. The eoracoids are very thin except in a transverse 



