﻿KIMMERIDGE CLAY. 



59 



§ 9. Ulna. — The proximal extension of the articular cup (PI. XVII, fig. 13, a ) upon 

 an anconal or olecranal production marks this bone as strongly as in Varanus (fig. 15, a) 

 but the excavation (?) of the shaft below the proximal end is differently situated. It 

 would seem as if the ulnar or outer border of that depression in Varanus (ib., fig. 15) 

 had been moved or extended palmad, in Omosaurus, toward the narrower, palmar, surface 

 of the bone ; and to such an extent that part of this excavation comes into view from the 

 ulnar side, as at c , fig. 14. This excavation is continued distad for more than half the 

 length of the bone ( c , c'). Below this part the shaft assumes a subtriedral form; and 

 its anconal border bends toward that aspect as it approaches the carpus. The articular 

 surface for this segment of the fore limb is wholly destroyed. 



§ 10. Manus. — Of the carpal bones have been extracted a left scaphoid, left cunei- 

 form, and left unciform. Of these three large wrist-bones the scaphoid is the smallest, 

 as in Varanus, not the largest, as in Crocodilus, in which it is connate with the trapezium 

 and trapezoides. 



The proximal surface for the radius is more uniformly and less boldly convex; the 

 opposite articular surfaces for the trapezium and lunare is more deeply concave. The 

 outer (ulnar) surface is elongate, narrow, and is the smallest on the bone ; it seems 

 barely to have touched the cuneiform, which is here, as in Varanus, the largest of the 

 carpals. 



The free broader radial surface of the scaphoid is flattened and roughened, and seems 

 to have continued, distad, the corresponding surface of the radius itself, which is on the 

 radial side of the distal end of that antebrachial bone (PI. XVII, fig. 8, g). 



The length (transverse extent) of the scaphoid is 5 inches ; the extreme (ancono- 

 palmar) breadth is 3 inches ; the extreme proximo-distal extent (on the rough flat 

 surface) is 1 inch 1 lines. 



The cuneiform is a massive cuboidal bone, with a proximal surface less concave for 

 the ulna than in Varanus, but with as deep an opposite (distal) concavity for the division 

 of the unciforme which supports the fourth digit. There is an approach to the croco- 

 dilian character of the bone in the increase of the distal part or surface. The transverse 

 extent of the bone there is 4 inches 9 lines ; that of the proximal surface being 

 4 inches ; the ancono-palmar diameter of the bone is 3 inches 9 lines ; the proximo- 

 distal diameter is 3 inches 10 lines. 



The unciform seems, as in the Crocodile, to have supported both fourth and fifth 

 metacarpals, not to have been divided to afford articulations for these bones on separate 

 portions. Its transverse extent in Omosaurus is 6 inches 4 lines ; the other dimensions 

 closely correspond with those of the cuneiform carpal. 



The digits of a hind foot are longer, as a general rule, than those of a fore foot in 

 existing Saurian Reptiles, and the same proportion has been demonstrated in the fore and 



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