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FOSSIL REPTILIA OF THE 



hind feet of some extinct Dinosauria. 1 The proportions, at least, of the metatarsals in 

 Hylaosaurus and Scelidosaurus support a belief that those of the metacarpals would be as 

 in the homologous bones of Iguanodon. 



Of the five metapodial bones of Omosaurus which have been wrought clear out of the 

 matrix not any show a length as compared with the breadth which exceeds that of the 

 metacarpal of the first digit in the fore-foot of Iguanodon (T. Ill, 1 m, Monogr. cit.) ; and 

 the homologues of the intermediate metacarpals are shorter in proportion to their breadth 

 than in Iguanodon. 



I conclude, therefore, that the above metapodials of Omosaurus are metacarpals, that 

 the digits were less unequal in length, and the whole fore-foot was more massive and 

 elephantine in its proportions, in Omosaurus than in Iguanodon. 



A metacarpal (PI. XVIII, figs. 3 — 6) has a flattened proximal surface (ib., fig. 5) of a 

 subtriangular shape, slightly convex near its radial (r) and anconal (a) periphery, slightly 

 concave toward the palmar border (p), which is broken away, the articular surface being 

 continued a short way upon the ulnar («) side of the shaft for junction with the 

 second metacarpal. 



The articular surface is pitted with small deepish depressions, as in most great 

 Saurians, where the joint surfaces seem to have been more syndesmosal than synovial. 

 The transverse and ancono-thenal diameters of the proximal surface are equal, each being 

 3 inches 6 lines ; but, had the ulnar border been entire, the transverse diameter would 

 have somewhat exceeded the other. 



The short thick shaft of this bone is three-sided ; one side extends obliquely from 

 the ancono-ulnar (fig. 3, aw) angle to the radio-palmar ( rp ) angle, with a transverse 

 convexity ; the second, or palmar, side (fig. 4, p) is less convex across ; the third, or 

 ulnar side, is flat across at the middle part, and somewhat concave near the two expanded 

 ends of the bone. All these surfaces are concave lengthwise, the palmar one least so ; 

 but the proximal half of this (fig. 4, p, p') has been crushed. 



The distal articular expansion (fig. 6), almost flat transversely at its anconal part (a), 

 begins to be concave at the middle of the distal surface (b), and this deepening to the 

 palmar one (p) divides the joint there into a pair of convex trochlear condyles. The 

 radial (?•, fig. 6) of these, when entire, would have been the most prominent of the two. 



The metacarpal (PI. XVIII, figs. 1 and 2) which supported the fourth digit has a 

 proximal articular surface of a more definite triangular figure (Plate XIV, fig. 5) ; the 

 anconal border ( a ) being the longest, and the angle between the radial (?•) and ulnar (k) 

 borders being rounded off. The articular surface is continued upon both these sides of the 

 shaft, but further for the articulation with the mid-metacarpal than for that with the fifth. 



1 Iguanodon, Pal. Monogr., ' Wealden and Purbeck Reptilia,' vol. for 1856, p. 1, tt. i, ii, iii (bind 

 foot) ; Iguanodon, Pal. Monogr., ' Wealden Reptilia,' vol. for 1871, p. 8, pi. iii (fore foot) ; Hylceosaurus, 

 Pal. Monogr., 1 Wealden Dinosauria,' vol. for 1856, p. 18, t. xi (bind foot) ; Scelidosaurus, Pal. Monogr., 

 Liassic Reptilia,' for 1866, p. 1", tt. x, xi (hind foot). 



