TIBIA OF HESPERORNIS. 91 



margin of the shaft, and is supported below by a strong rounded ridge, 

 •which, lower down, passes into the true fibular ridge. There is a strong 

 epicnemial crest- on the anterior surface of the proximal end, which, above 

 the articulation, rises into a powerful tuberosity, or cnemial process. To 

 the outer posterior surface of this spine, the patella was attached (Plate XX). 



The shaft of the tibia is nearly straight, with its transverse, slightly 

 greater than its fore and aft, diameter. Seen from in front, the outer margin 

 appears slightly concave, and the inner margin convex. The fibular ridge 

 is strongly developed, and can be traced along the proximal three-fotu'fhs 

 of the bone. Just below the middle, it disappears for a short distance, 

 being cut off by an oblique groove for the artery, which here passed 

 between the tibia and fibula. In the type specimen, number 1200, the 

 surface of the shaft is marked by delicate vascular impressions, which are 

 imperfectly indicated in Plate XIV, figure 1. In the specimen itself, these 

 impressions are as perfect as in life, and well illustrate the marvelous 

 degree of preservation characteristic of the vertebrate fossils from this 

 geological horizon. 



The surface of the tibia shows no pneumatic foramina, but there is a 

 rather large medullary cavity in the shaft. The size of this cavity is 

 shown in the accompanying cuts, which represent transverse sections' of 

 the tibia near the middle, and near the distal end. 



.DIG. Zb. 



2v" 



Figure 2 fi.— Transverse section through middle part of tibia of Hesperornis regalis ; (No. 120T), top v 



natural size. 

 Figure 27. — Transverse section through same bone; (No. 1491), near distal end; same view; natural 



m. medullary cavity ; /. fibular ridge. 



The distal end of the tibia resembles that of the same bone in Podieeps, 

 but the inner condyle is here much the larger, and the two are only moder- 

 ately expanded. The inner condyle extends somewhat below the outer 

 one, but its fore and aft diameter is much less. The transverse diameter of 



