THE AMERICAN NATURALIST. [Vol. XXXVII. 



parts in the skeleton of the legs in grebes and loons. This 

 has also been noted by Stejneger, and Marsh said in his 

 Odontornithes that the "posterior limbs of Hespcrornis regalis 

 present an admirable example of adaptive structure. The 

 means of locomotion were confined entirely to these extremi- 

 ties, and the life of Hesperornis was probably more completely 

 aquatic than that of any known bird. It may fairly be ques- 

 tioned whether it could even be said to walk on land, although 

 some movement on shore was of course a necessity. Considering 

 the posterior limb as a whole, it will be found a nearly perfect 

 piece of machinery for propulsion through the water. Provision 

 was made for a very powerful backward stroke, followed by a 

 quick recovery, with little loss by resistance, a movement quite 

 analogous to the stroke of an oar, feathered on its return. 



"Among recent birds, we have, in the genus Podiceps, the 

 nearest approach to the legs and feet of Hesperornis, and the 

 osseous structure of these parts is essentially the same 

 throughout in the two genera. The muscular system, also, of 

 this member must have been very similar in both. In many 

 respects, however, the bones of the posterior limbs of Hes- 

 perornis present evidences of a more primitive structure than 

 is seen in any recent diving birds." 



The femur was remarkably short and stout, being flattened 

 in the antero-posterior direction. The large, rounded head was 

 supported by a short, strong neck, and excavated above by a pit 

 for the ligamentum teres. Trochanter major was large, and the 

 entire proximal end of the bone possessed an articular surface 

 for the antitrochanter. As in Urinator, the shaft was curved, 

 and exhibited strong prominences for muscular insertion. 

 Expanded distally, the outer condyle was the larger of the two, 

 and only a shallow groove divided it from the inner one. 



Tibiotarsus was a long, powerful bone, by all odds the big- 

 gest one in the skeleton of this bird. It much resembles the 

 same bone of the leg in any of our typical grebes. At its dis- 

 tal end, as in Podiceps, there is no osseous bridge in front span- 

 ning the longitudinal muscular groove below. 



A very large free patella was developed, and it was pierced 

 by a foramen to transmit the tendon of the ambiens muscle, as 



