54 



MEMOIRS OF THE CARNEGIE MUSEUM 



Principal Measurements of the Different Elements of the Foot. 



Greatest width of astragalus 260 mm. 



" depth " " ...160 



' ' length of metatarsal 1 210 



" " " " II 207 



" " " " III 215 



" " " " IV 190 



" " " " V 160 



" " " ungual phalanx of digit 1 235 



" " " " " " " II 136 



" depth " " " '' " 1 175 



" " " " " ■ " " II 105 



10 1 in. 



6i " 



7 V a 

 'T5 



c 5 a 



9 i " 



61 " 



Internal Structure of Limb Bones. 



Marsh has described the hmb bones of the Sauropoda as soHd and has considered 

 this character as of subordinal value. 



A careful examination of cross sections made at almost any point in any of the 

 larger limb bones of the Sauropoda will show that they are not solid, but consist ex- 

 ternally of a comparatively thin portion of rather dense, hard bone, grading off quite 

 suddenly into a cancellated structure. This becomes more openly cancellate toward 

 the interior, and there is formed in the center of the shafts of the larger bones dis- 

 tinct cavities quite devoid of osseous matter. Such conditions are especiall}^ preva- 

 lent in the femora. See Fig. 23, a, b, c, from photographs of cross sections taken at 

 different points of the left femur of No. 94. 



Taxonomy. 



Marsh has elevated the Dinosauria to the rank of a subclass, dividing the dif- 

 ferent genera into three orders. One of these, the Theropoda, includes all the car- 

 nivorous Dinosauria, while the herbivorous forms are placed in two orders, the 

 Sauropoda and the Fredentata. 



The Sauropoda, to which Diplodocus belongs, are the least specialized of the three 

 Dinosaurian orders. This order embraces several genera, chiefly from the Jurassic 

 of North America, while a few forms have been described from the Jura of Europe 

 and the Cretaceous of India, and two or three imperfectly known genera from the 

 Cretaceous of South America have been assigned to the Sauropoda, though some of 

 these latter forms may perhaps yet prove to belong to the Fredentata rather than the 

 Sauropoda. 



Diplodocus was the most specialized member of the Sauropoda. This specializa- 

 tion is seen in the elongated caudal and cervical regions and the abbreviated dorso- 



