Yol. 6g.~] SKELETON OF OliXITHODESMUS LATIDENS. 391 



The Metacarpal. 



The proximal end of the ulnar metacarpal is well seen in the 

 Atherfield specimen No. 1 (PI. XXXIX, fig. 10) ; and the distal 

 is fairly well seen in the Atherfield specimen Xo. 2. Its exact 

 length cannot positively be determined, for a portion of the shaft 

 is missing. If we judge from the great size of the proximal end 

 and the much reduced distal extremity, and produce their borders 

 at the required angles to connect them, its length would. seem to 

 be about 215 mm., 1 or roughly half that of the ulna :■ this is 

 far from what it should be, if it followed the structure of the 

 short-tailed forms, where the metacarpal is not shorter than the 

 antebrachium. However, in Ornithostoma, 2 which is short-tailed, 

 ' the bones of the forearm [are] . . . shorter than [the] wing- 

 metacarpal.' The proximal end is remarkably robust, and occupies 

 the full width of the distal carpal articulation. From the preaxial 

 side, the articular surface is convex for two-thirds of its extent ; 

 this is followed by a deep valley. Postaxially to this, is a flattened 

 oval facet (PI. XXXIX, fig. 10, A), which does not look proximally 

 as the others do, but has its ventral edge raised and the dorsal 

 depressed, so that its articular surface is oblique to them, and looks 

 outwards and upwards. Half of its area lies outside the line of the 

 postaxial border of the bone, although that border branches out 

 and supports it. When the two-thirds are in articulation with 

 the distal carpal, this facet is free, and thus takes no share in the 

 joint. It articulates with the flattened oblique facet, proximal to 

 the main articulation of the distal carpal on the dorsal surface of 

 that bone (PI. XXXIX, fig. 9, A), and then only when the meta- 

 carpal is directed backwards, and is rotated in a postaxial direction. 

 Such a position would be assumed in folding the wing. The distal 

 articulation is an obliquely -placed trochlea ; it is very similar to 

 the examples of this end of the metacarpal from the Cambridge 

 Greensand, figured by Owen and Seeley. The dorsal and preaxial 

 borders of the bone are moderately convex. The dorsal surface at 

 the proximal end possesses a deep concavity on each side, and a 

 convexity in the centre, which gradually dies away distally. The 

 proximal lateral borders of the bone are much raised, especially 

 on the preaxial margin. Within this area (PI. XXXIX, fig. 10, C), 

 the splint-like small metacarpals were situated ; their position 

 is above the plane of the ulna, and in the same line as the 

 radius. The small metacarpals are only preserved as fragments ; 

 the proximal end of one is lying in the concavity on the dorsal 

 surface of the wing-metacarpal. It is a very small rod-like bone, 

 with a little thickening at the articular end pre-postaxially, and 

 a convex articular, surface. Their number is not known. 



1 As before mentioned, the bones of the Atherfield specimens are equal 

 in size. 



2 S. W. Williston, 'Eestoration of Ornithostoma (Pteranodcii) ' Kansas 

 Univ. Quart, ser. A, vol. vi (,1897) p. 51. 



Q. J. G. S. Xo. 274. 2 d 



