144 Field Columbian Museum — Geology, Vol. II. 



Fig. 3). It resembles that of Nyctosaurus, though having a less elon- 

 gated process beyond the articular lateral emargination. The figures of 

 the carpal bones of Ornithocheirus given by Seeley (Ann. Mag. Nat. Hist. 

 Aug. 1870, and Dragons of the Air, p. 124) closely resemble these bones. 

 Professor Seeley says of the " lateral carpal ": " It is a flat, oblong bone, 

 attached to the inner side of the distal carpal, and, instead of being pro- 

 longed distally in the same direction as the other metacarpal bones, is 

 turned round and directed upward, so that its upper edge is flush with the 

 base of the radius, and gives attachment to the pteroid." I had supposed 

 that the larger end, as shown in the present figure, fitted into the interval 

 between the two carpals, and that the emargination was for the articulation 

 of the rounded head of the pteroid, though perhaps the position assigned 

 to it by Seeley is the correct one. The bone is thin on the sides shown in 

 the figure, so that the articulation of the pteroid must have been either in 

 the emargination or with the broader end. Marsh says* that it " stands 

 nearly at right angles with the wrist," and I am inclined to think he was 

 right. The structure of these wrist bones is almost identical with what it 

 is in Pteranodon. 



measurements of. carpal bones. 



mm. 



Length of articulated carpus 15 



Greatest diameter of distal carpal 24 



Lesser diameter of same 14 



Greatest diameter of proximal carpal 26 



Length of "lateral carpal" 17 



Width of same 8 



Metacarpals. The first metacarpal, or pteroid (PI. XLII, Figs. 4, 5), 

 is an elongated, pointed, styliform bone, with an enlarged articular car- 

 pal extremity. In both arms this bone has been displaced, though so 

 closely associated with the corresponding extremity that the position is 

 assured. Its articular end is broad, its margin nearly at right angles with 

 the long axis of the bone. The articular surface is nearly at right angles 

 with the transverse diameter, in life nearly circular in outline, and decid- 

 edly convex. It is separated from the bone by a slight constriction. 

 The dorsal border of the bone is very gently concave throughout, and 

 the inferior border is correspondingly convex for the greater part of its 

 extent. The pteroid of the right arm is lying close to the lateral carpal, 

 as though its articular surface fitted into the lateral emargination of that 

 bone in life. Oscar Fraas was the first, so far as I can learn, to recognize 

 the real nature of this bone as belonging to the first digit,f a view after- 

 wards adopted by Marsh and Zittel. . 



♦Amer. Journ. Sci., 1882, p. 255. * 



fPaleontographica, 1878, p. 170. 



