50 



MEMOIRS OP THE CARNEGIE MUSEUM 



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posed to the ground when the animal stood erect. A superior view of the astrag- 

 alus is shown in Fig. 20. 



TliG Metatarsus. — As in Brontosaurus the metatarsus of Diplodocus is composed 

 of five well-developed functional metatarsal bones. Of these I. and II. are much 

 stronger than III., IV. and V. and formed in life the chief support to the hind 

 limb. Metatarsals III., IV. and V. are comparatively slender, more so than are the 

 same elements in Brontosaurus, as compare Figs. 20 and 21. The two latter were 

 opposed to the distal end of the fibula and not to the astragalus. Metatarsal I. is 

 the shortest and strongest of the series. It is constricted medially, expanded verti- 

 cally at the proximal, and laterally at the distal extremity, as are also the other 

 metatarsals. Metatarsal II. is considerably longer and more slender than I. Met- 

 atarsal III. is the longest in the series, though IV. 

 and V. are only slightly shorter. Metatarsal IV. 

 is the more slender of the series, while V. is much 

 more robust and presents a rather broad and rugose 

 distal surface. 



The Phalanges. — These will best be described by 

 commenciog with those of the first digit and con- 

 sidering each serially from the first to the fifth. 

 The first digit supports two phalanges, one, the 

 proximal, is short, broad and deep, and supports 

 distally a very large, long, deep, curved and com- 

 pressed claw-like ungual which in life Avas evidently 

 enveloped by a horny sheath, as is evidenced by 

 the grooved and pitted external surface. The 

 second digit supports three phalanges. The proximal is rather longer than that 

 of digit I. and with the three dimensions subequal. It is stout, with its inner 

 side nearly perpendicular, while externally the surface slopes downward and out- 

 ward, terminating inferiorly in a rather sharp ridge. The succeeding phalanx 

 is reduced to a rather flat wedge of bone about one inch in thickness on its 

 internal side and reduced to a sharp thin wedge externally. It is thus intro- 

 duced as a rather thin wedge between phalanges one and three. The latter is 

 rather large and much compressed ungual, differing chiefly in its smaller size from 

 that of digit I. Both these unguals show an extensive proximal articular surface 

 indicative of a considerable vertical movement of these phalanges. They are also di- 

 rected rather sharply outward as well as forward. The proximal phalanx of digit III. 

 is slightly longer than broad, while its other two dimensions are subequal. Phalanx 





FiGt. 20. Superior view of asti'ag- 

 alus of right pes of Diplodocus carnegii 

 (No. 94). f, surface for articulation 

 with tibia ; /, surface for articulation 

 with fibula ; p, posterior side. One 

 fifth natural size. 



