20 PROCEEDINGS OF THE NATIONAL. MUSEUM vol.81 



The principal measurements of the fore limb are as follows : 



Mm 



Humerus, length 1, 010 



Humerus, least circumference 440 



Ulna, length 740 



Ulna, least circumference 295 



Radius, length 690 



Radius, least circumference 244 



The missing fore feet have been replaced by casts furnished by the 

 Carnegie Museum, whose composition is based, according to Hatcher, 

 upon specimens and descriptions kindly furnished by Dr. H. F. 

 Osborn, of the American Museum of Natural History. 



Positive determination of their correctness is still wanting, for 

 these elements are missing in the five more or less complete skeletons 

 of Diplodocus now known. The feet as they came to us were pro- 

 vided with three terminal j)halanges, but in the present mount all 

 but the first have been omitted for the reason that on the many 

 articulated fore feet now known of sauropodous dinosaurs never has 

 more than one clawlike ungual been found and that on Digit I. It 

 therefore seems reasonable to suppose that Diplodocus had a sim- 

 ilarly constructed manus. In fact, in a foot attributed to Diplo- 

 docus described by Osborn ^^ mention is made of a single terminal 

 phalanx only. 



Hind limb. — The right hind Jimb, including the tarsus and pes, 

 was found complete and articulated. The femur when compared 

 with that of D. carnegii (C. M. No. 84) is relatively slenderer, and 

 the two ends are much less expanded, as is clearly indicated in the 

 table of comparative measurements. Otherwise the two bones are 

 in accord. Although the present femur is slightly longer than either 

 of those of the Carnegie Museum specimen, the tibia is slightly 

 shorter. However, these differences in length are so slight as to be 

 readily accounted for by individual variation, or perhaps they are 

 due to elongation through pressure from the weight of superimposed 

 strata. The tibia and fibulae are of the elongated type typical of 

 the relatively slender-limbed Diplodocus. 



The osseous portion of the tarsus consists of the astragulus only. 

 The pes is complete and displays the digital formula 2, 3, 3, 2, 2. 

 Digits I, II, and III are terminated by clawlike unguals that pro- 

 gressively decrease in size toward the outer side of the foot. The 

 ungual of Digit I has much of the tip missing, probably on account 

 of an injury during life, since the end is rounded and healed. The 

 presence of a small clawed ungual on the third toe fully confirms 

 Hatcher's surmise that such a bone existed, although it was missing 

 from the specimen studied by him. 



» Bull. Amer. Mus. Nat. Hist., vol. 14, p. 205, 1901. 



