488 



GEOLOGY OF THE DEXVER BASIX. 



distinctive character of these vertebrae. A more important character of the 

 same centra is a very large cavity in each side, connected with the outer 

 surface by an elongated foramen below the base of the neural arch. The 

 inner surface of this cavity indicates that it was not tilled by cartilage, and 



lii, :;i. I.. It femur of Atlantosauru.i immanU Marsh; inner view. 



Fig. 34ft. — Proximal end of same. 



Fio. 35.— The same bone ; front view. 



Fig. 35a.— Distal end of .same. 



All (he figures are one-sixteenth natural size. 



c, inner condyle; c' t outer condyle; /, groove for fibula; ft, head; t, trochanter; r, lower trochanter. 



it was, perhaps, a pneumatic opening, designed to lessen the weight of the 

 enormous sacral mass. The transverse processes, or more strictly speaking, 

 the sacral ribs, of these vertebrae are very stout and of moderate length. 



