52 



MEMOIRS OF THE CARNEGIE MUSEUM 



It is interesting to note that while in the MammaHa digit I. it is the first to become 

 obsolete, in the Dinosauria the reduction would seem to have commenced in the pes 

 with the fifth, while the first digit appears as functionally the most important of the 

 series. Though there are only two phalanges supported by it these are exceptionally 

 well developed. Commencing with digit I. the normal number of phalanges on 

 any digit in the pes of Dijolodocus is as in most birds, always one more than the 

 number of such digit. Thus the first digit has two phalanges, digit 11. has three 

 and the third digit has four. But in digits IV. and V. the number of phalanges 



VVJ.Carpenter 



u 



Fig. 22. Front view of right hind foot of Brontosaurus excelsus Marsh (No. 89). 



are reduced to two and one respectively b}'^ atrophy due to disuse. There can be 

 little doubt that as regards the hind feet Diplodocus walked on the inner side of the 

 feet with the large terminal claws directed very strongly outward. The above de- 

 scription of the pes and hind limb of Diplodocus is based upon a right femur of No. 

 84 and a left femur and right tibia, fibula and foot of No. 94, complete except for 

 the ungual phalanx of digit III. and the solitary phalanx of digit V. The principal 

 characters are well shown in Fig. 21, while Fig. 22 shows a foot of Brontosaurus for 

 comparison. 



