hatcher: diplodocus (marsh) 51 



two is a short wedge-shaped bone about one inch long on its internal lateral margin 

 and ending in a sharp lateral ridge externally. Just beneath this bone in No. 94 

 of our collections, and adhering to it, there was found a very small and rather flat 

 bone which may have been either a rudiment of a third phalanx or a sesamoid. 

 Its position would seem to indicate the latter, though quite similar rudimentary 

 third phalanges are known to be present in the third digit of Brontosawus. I there- 

 fore interpret it as a rudimentary third phalanx. There was evidently a well-de- 

 veloped and functional ungual, or fourth phalanx, terminating digit III., although it 

 was not recovered. In digit IV. the phalanges are reduced to two in number. Of 

 these the proximal is much the larger. It is rather depressed, but laterally ex-. 



Fig. 21. Front view of right hind foot of Diplodocus carnegil (No. Oi). a, astragakrs. 



panded distally, and supports a small, rounded, hemispherical terminal phalanx 

 which in life was without horny covering and was probably imbedded within the 

 integument of the skin. No phalanges were found in position with the fifth meta- 

 tarsal, but as in Brontoscmras there was most likely a small, rudimentary first phalanx 

 without nail. 



From the above description and accompanying figures it will be seen that the pes 

 of Diplodocus is semi-plantigrade and that the weight of the body was borne by the 

 inner side of the foot, so that digits one and two became correspondingly larger, 

 while three, four and five through disuse have become more and more atrophied. 

 Although in Diplodocus this had not yet resulted in the total elimination of any of 

 the digits, yet the phalanges of the fifth have already become functionally obsolete. 



