n Pachiz/ioif from the Camhruhje Upper Oreeusand. 313 



bone, and then al»ruj)tly terininatts. The external side is 

 nearly strai_«;ht between the artienlations, and convex from 

 above downward; bnt towards the distal end an inHatinn aj)- 

 pears towards tlie nj)per part, so as to make it approximate in 

 outline to a vertically ehm^Mted oval. The least measure- 

 ments of the shaft behind the distal articulation are less than 

 1^ inch from side to side, and Irss than 1^ inch from al)ove, 

 downward, l^eyond this the distal articulation expands but 

 little, measurin;j:, as preserved, 2 inches from above down- 

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

 articulation in the other bones is transversely oblone^, in tliis 

 fifth digit it is vertically ol)long. It is an inference, perhaps 

 not unworthy of considerati<tn, that since the deposit yields 

 two kinds of claws ])resumably Dinosaurian, one depressed as 

 in Chclonians, the other com})rcssed as in Lizards, the former 

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

 the*^ fifth. 



In size and form of the bones this metapodium suggests 

 comparison witb the pachypod mammals, and most conspi- 

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

 which the metajxxlial 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 jiresevved 

 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 re])re- 

 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 tliat 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 Avould not so 

 steadily decrease in size. In ItJunoeeros and Jfippopotainits 

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

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



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

 to me, is there any structure in fore or hind limb M-hich can 

 be compared with this metapodium of AcantJwphoh's. 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, which the 



Ann. d' Mag, N. Hisf. Ser. 4. Vol. viii. 24 



