a Pachy pod from the Cambridge Upper Greensand. 313 



bone, and then abruptly terminates. The external side is 

 nearly straight between the articulations, and convex from 

 above downward ; but towards the distal end an inflation ap- 

 pears towards the upper part, so as to make it approximate in 

 outline to a vertically elongated oval. The least measure- 

 ments of the shaft behind the distal articulation are less than 

 Ig- inch from side to side, and less than 1^ inch from above 

 downward. Beyond this the distal articulation expands but 

 little, measuring, as preserved, 2 inches from above down- 

 ward, and one inch from side to side ; so that while the distal 

 articulation in the other bones is transversely oblong, in this 

 fifth digit it is vertically oblong. It is an inference, perhaps 

 not unworthy of consideration, that since the deposit yields 

 two kinds of claws presumably Dinosaurian, one depressed as 

 in Chelonians, the other compressed as in Lizards, the former 

 may have belonged to the first four digits, and the latter to 

 the fifth. 



In size and form of the bones this metapodium suggests 

 comparison with the pachypod mammals, and most conspi- 

 cuously, by the presence of five digits, with the elephant, in 

 which the metapodial bones are equally large. But in the 

 elephant the bones of the fore foot are larger than those of the 

 hind foot, contrary to the rule with Dinosauria. An elephant 

 would similarly have had the proximal ends of the bones 

 transversely truncated ; the proximal ^ end would similarly 

 have had a great depth from front to back, and have preserved 

 the same width from side to side. The form of the distal end 

 would have been the same, though the slight mesial depres- 

 sion of that articulation in the fossil would have been repre- 

 sented by a slight mesial elevation in the mammal. The 

 bones would not have obliquely overlapped at the proximal 

 end in the elephant; and in that animal the large massive 

 bone would have been the fifth, and not the first as I have 

 named it, and the shafts of the other bones would not so 

 steadily decrease in size. In Itliinoceros and Hippopotamus 

 the bones conspicuously have a tendency for the inner to over- 

 lap the outer at the proximal ends as in the fossil. 



Among birds, not even among foetal birds, so far as known 

 to me, is there any structure in fore or hind limb which can 

 be compared with this metapodium of Accmtliopholis. Coming 

 to crocodiles, there is a similar gradational decrease in size of 

 the shaft in bones 1 to 4 in the hind limb ; but then in croco- 

 diles the fifth bone is wanting, and the bones are out of all 

 proportion too long. In the fore limb, however, there are five 

 digits, and the proportions of the bones match much better 

 what is seen in the fossil ; the angle, however, Avhich the 



Ann. & Mag. N. Hist. Ser. 4. Vol.xm. 24 



