FEET OF HESPERORNIS. 101 



more compressed transversely. The articulation of the proximal end is 

 similar to that of the preceding phalanx, but the outer facet has encroached 

 considerably on the inner, which is thus materially narrowed. The exca- 

 vation on the outer inferior margin of the shaft is deep, and continues to 

 the distal extremity. The tubercle on the distal end is prominent, and its 

 apex is obliquely truncated. The remaining articular surface is less convex 

 than in the phalanx last described. 



The third phalanx (Plate XVIII, figure 3) of the fourth digit is almost 

 precisely equal to the second ha length, but is more slender in its remaining 

 proportions. It is much more compressed transversely than the second, 

 and the two articular faces of its proximal end are more nearly equal. 

 The tubercle on the distal end is much like that in the preceding phalanx, 

 but the remaining articular siu-face is smaller, and less convex. The 

 outer inferior excavation of the shaft materially diminishes the weight 

 of this bone. 



The foiu-th phalanx (Plate XVIII, figure 4) of the outer digit is long 

 and slender, and much compressed, especially at its distal end. The outer 

 articular face of the proximal extremity is narrow, but much larger than 

 the inner. The latter is vertically oval in outline, and confined to the 

 superior half of the face. Seen from above, this bone gradually tapers 

 from its proximal to its distal end, but the outer view shows that the sides 

 of the shaft are nearly parallel. The outer inferior surface is slightly 

 concave, and the distal extremity is truncated, nearly at right angles to the 

 axis of the shaft. 



The articular face on the lower extremity has almost entirely lost the 

 crescent and peg structure, and resembles the distal articulation of the 

 phalanges in ordinary birds and reptiles. The compression of this bone, 

 and modification of its articulation, permit the partial rotation of the 

 digit, so that when at rest, the flattened extremity was nearly horizontal. 

 A similar structure is seen in the other digits. The same relative position 

 of the toes was maintained in the backward stroke, but in the recovery, 

 the foot was turned edgewise, and the digits followed each other in the 

 same vertical plane, the outer being in advance. 



