314 Mr, H. G. Seeley 07i xA.canthopliolis platy]3us, 



proximal end of the bone makes with the distal end is greater 

 in crocodiles than in AcanthojyJwUs, and the fifth bone is 

 shorter and of different shape. In the Nilotic Monitor the 

 metapodium includes five elements in both front and back 

 limbs, but only in the front limb is the fifth bone compressed 

 at all as in the fossil ; and in the hind limbs the bones are 

 elongated as in the crocodile ; and in neither limb is there a 

 gradational decrease in the size of the shaft from within out- 

 ward. Nor is there a nearer resemblance in Uromastix^ Stellio, 

 Lacertaj Polychrous, Iguana^ DracOy or any of the typical 

 lizards with which I am familiar. 



Among the Emydian Chelonians, of numerous genera the 

 metapodium similarly shows a gradational decrease in the size 

 of the bones from the first to tlie fifth, with similar proportions 

 for each bone, a similar overlap of the proximal ends, and 

 similarly shaped articular surfaces. 



Among frogs the bones gradationally increase from the first 

 to the fifth ; but the overlap of the proximal ends is usually 

 discernible, so that the right and left feet could not be con- 

 founded. 



From these comparisons it would seem that the only living- 

 animals which throw light on the structure of the foot in 

 Acanthopliolis are the Elephant, Emydians, and Crocodiles. 

 Since the fossil bones have no epiphyses, have the rejatilian 

 form of distal articulation, and have the bones aiTanged in 

 their relation to each other and to the limb in a markedly 

 reptilian way, it seems probable that the resemblances to tlie 

 elephant, close and curious as they are, must be classed as a 

 functional modification, and not as a mark of organic ajjproxi- 

 mation of the Dinosauria towards the Mammalia, tliough 

 with our present imperfect knowledge it may not be easy to 

 estimate the influence of such a pachypodial function in in- 

 ducing differentiation of the higher vital tissues. The com- 

 parison, then, is limited to Emydians and Crocodiles ; and, in 

 view of the pachypodial function of the Emydian limb, it will 

 not be surprising if that type is found to be the nearer to 

 Acanthopholis : nevertheless the resemblance of the fore foot 

 of the crocodile is such as might well make any one pause in 

 doubting its crocodilian affinity ; for in a case where the func- 

 tions of the parts were presumably dissimilar and the struc- 

 tural resemblance not unlike in both, the affinity is presumably 

 strongest genetically Avhere the functions of the parts are dif- 

 ferent. In this case such a view would make the crocodilian 

 resemblance at least as important as the resemblance to Chelo- 

 nians. Yet as the Dinosaurian type would, from our present 

 palffiontological knowledge, seem to be at least as old as the 

 recent monimostylican Reptilia, the resemblance throws no 



