VERTEBRAL RIBS OF HESPERORNIS. 63 



Measurements of Humerus. (No. 1206.) 



Length of humerus, 152. mm 



Greatest diameter of shaft, 7.0 



Transverse diameter of shaft, 2.2 



Greatest diameter of proximal end, 11.5 



Greatest diameter of proximal articulation, 10.5 



Transverse diameter of proximal articulation, 5.0 



Greatest diameter of distal end, 6.0 



The Vertebral Ribs. (Plates IX and XX.) 



The ribs of Hesperornis present no marked features to distinguish 

 them from those of modern birds. They are composed of dense bone, but 

 some of them contain irregular cavities. The articulated vertebral ribs of 

 Hesperornis regalis are nine in number, on each side. The first three of 

 these were attached to the last three cervical vertebrse, and had their distal 

 ends free. The remaining- six are all well developed ribs, which were 

 connected b y means of the sternal ribs with the sternum. 



The First Rib (Plate IX, figure 1) which is free in Hesperornis 

 regalis was attached to the fifteenth vertebra, and is quite short. The head 

 (capitalum) and tubercle (tuberculam) are both well developed, and the 

 branches which support them stand nearly at right angles to each other, 

 the neck of the rib being about twice the length of the tubercular support. 

 The descending part of the rib below the tubercle tapers rapidly, and 

 ends in a sharp point, scarcely below the body of the vertebra. 



The Second Rib in this species (Plate IX, figure 2) was supported by 

 the sixteenth vertebra, and is very much larger than the first. The 

 branches sustaining the head and tubercle meet at an angle less than a 

 light angle, and both articular facets are well developed. The shaft of this 

 rib is stout, somewhat curved, and, when in its natural position, it 

 descended nearly perpendicularly, ending in an obtuse free extremity. 



The Third Rib (Plate IX, figure 3) is the last free rib, and was sup- 

 ported by the seventeenth, and last cervical, vertebra. It is longer than 

 the preceding one, and, when in position, its shaft stood nearly vertical. 



