470 



RICHARD SWANN LULL ON 



or it luav be a continuous, straight line impressing during the whole of the animal's walk 

 or just before sitting on its heels as in the case of Anonioepus intermedins. The occa- 

 sional impression of a mauus is another distinguishing character and the presence of irreg- 

 ular dermal scutes or tubercles upon the skin, though rarely leaving a record, is certainly 

 not avian. 



Relation of pads to interjihalangeal joints. — The generalized arrangement of the 

 pads, which, with the exception of the distal articulation, are mesarthral. that is. they 

 he opposite the phalanges as in the human hand and not arthral with the jmds opposite 

 the joints, as in all lizards and the majority of carinate birds, characterizes the earlier 

 dinosaurs. That this interpretation of the morphology of the foot is correct seems true 

 for several reasons. The foot bones of Anckisaurus colurus, which is clearly to be corre- 

 lated with the track, Anchisaurijms dananus, will only lie in the impression in one way 

 and that brings the pads mesarthral in position. Hatteria seems to have mesarthral pads, 

 certainly they ape not arthral and Hatteria's foot must approximate that of the dinosaurs 

 more than any known form. Finally in certain of the Limicolae, namely Phalaropus 

 hyperhoreus ^ in which the foot retains its cursorial character without having become 

 specialized for perching, the pads are arranged as in dinosaurs. The rhea has anotlier 

 form of specialization, for here the pads become confluent and hence fewer than the over- 

 lying bones, giving no clue to the phalangeal formula, especially on digit W . It seems 

 probable that among the later Iguanodont dinosaurs there was a coalescence of pads 

 correlated with increase in weight as in the rhinoceros. The tracks of Iguai^odon itself, 

 which are known, conform with this belief. 



Hitchcock's view that the distal pad of each digit covers l)oth the penultimate and 

 the proximal end of the ungal phalanges is tmdoubtedly correct. When viewed from the 



side the ungal phalanx shows a groove running 

 from the point backward midway between the upper 

 and lower borders until it reaches a point about half 

 the length of the bone in a walking digit and farther 

 backward in a grasping one. Another sinuous 

 depression which takes a forward and downward 

 course across the bone defines the hinder limit of 



Fig. 1. Wgit II of l)iiiiodosauni.s viewed in 

 profile with the outline restored to, show the 



relation of the claw and pads to the phalanges, the claw sheatli, while into the grooves first men 



From a cast in the collection of the American 

 museum of natural history. X k- 



tioned, fit ridges on the inner surface of the claw 

 and serve to hold it firmly in place. The fleshy 

 part of the digit extending somewhat beyond the root of the claw thus covers a greater 

 or less portion of the phalanx itself as well as that just within (lig. 1). In cases where 



' Cones, Key to North American birds, 1884, fig. 63 his. 



