STERNAL RIBS OF HESPERORKIS. 65 



The Seventh Rib (Plate IX, figure 7) has a prominent head, placed 

 on a slender neck, and the tubercular facet is merely a flat articular tract 

 on the upper surface of the bone. This rib is considerably longer than 

 the preceding, and its upper half is more curved. The lower half is 

 nearly straight, and is flattened transversely. It supported a large 

 uncinate process, which had a rather slender neck, and an expanded distal 

 half, bent upward at a slight angle with the general axis of the bone 

 (Plate IX, figure 14). The distal extremity of this rib is wider than the 

 shaft, and horizontally truncated. 



The Eighth Rib (Plate IX, figure 8) is very similar to the last, but 

 is somewhat longer. The neck is very slender, and the tubercular facet 

 has almost entirely disappeared. At the end of the upper fourth of this 

 rib, there is an abrupt inward curve, and from this point to the lower 

 extremity, the shaft is nearly straight, in the specimen preserved, and in 

 its proportions is very much like that last described. This rib bears a 

 very small uncinate process (Plate IX, figure 15), which is considerably 

 curved upward, and is the last of the series. 



The Ninth Rib (Plate IX, figure 9) is of about the same length as the 

 preceding, but much more slender. It has no true tubercular face, and 

 no uncinate process. Its shaft is nearly of equal width throughout its 

 whole extent, and the distal end is not expanded. Its lower extremity is 

 truncated at right angles to the shaft, and roughened for cartilaginous 

 attachment with a slender sternal rib. 



The Sternal Ribs. (Plates IX and XX.) 

 In Hesperomis regalis, there are four sternal ribs which articulated 

 directly with each costal border of the sternum, and on this are four well 

 developed processes for the union. Behind these true sternal ribs, were 

 two others, which, as in many recent birds, united together at then- lower 

 attenuated extremities, and were thus attached to the preceding sternal 

 rib by cartilage. In Hesperomis crassipes, there were five sternal ribs on 

 each side articulating with the sternum. 



