WINGS OF ICLITHYORNIS AND APATORNIS. 155 



mal articular surface bears a resemblance to that seen in Graculus, differing 

 from that of Iclithyornis in being- grooved along its ulnar side. The groove 

 terminates in a distinct, though shallow, pit at the base of the ulnar, 

 or third, metacarpal. 



Of the three united metacarpals, the first is shorter than in Iclithyornis, 

 and hardly extends beyond the end of the upper one-fifth of the bone. 

 Proximally, it is well elevated, extending to a height almost equal to its 

 length. The articular face is nearly as in Iclithyornis. 



The middle metacarpal is less robust than in Iclithyornis, but is still 

 short and strong, as compared with the same bone in many living birds of 

 flight, but does not differ greatly from that seen in Sterna. The tubercle 

 near the proximal end of the palmar surface is well developed. The 

 groove seen along the distal half of the anconal surface in Iclithyornis is 

 comparatively ill defined, and the tubercle near the distal end of this 

 surface in that .genus is very rudimentary, or only faintly indicated. The 

 distal end is much less expanded than in Iclithyornis, and the articular 

 surface comparatively smaller. 



The outer or third metacarpal is more slender and flattened than in 

 Iclithyornis, and bears, on its palmar surface, near the proximal end, a low 

 but distinct tubercle for muscular attachment. 



The more important dimensions of the united metacarpal % bones in 

 Iclithyornis and Apatornis are given below : 



Measurements of Metacarpal. {Iclithyornis dispar, No. 1450.) 



Greatest diameter of distal end, 5.5 mm 



Transverse diameters of distal end, 4.0- 2.8 



Diameters of shaft of second metacarpal element, 3.5- 2.2 



Measurements of Metacarpal. (Ichthyornis dispar, No. 1730.) 



Length of metacarpal, 31.5 mm 



Greatest diameter of proximal end, 9.6 



Transverse diameter of proximal end, 3.2 



Greatest diameter of distal end, 6. 



Transverse diameter of larger articulation, 5. 



Length of first metacarpal element, - 5.2 



