MAHSH.] 



BRONTOSAURUS. 



171 



statement that any of the species lias the sacrum solid is evidently 

 based on erroneous observation. 



Another peculiar character of the sacrum in the present genus is its 

 lofty neural spine. This is a thin, vertical plate of bone with a thick 

 massive summit, evidently formed by the union of the spines of several 

 vertebrae. In front it shows rugosities for the ligament uniting it to 

 the adjoining vertebra, and its posterior margin likewise indicates a 

 similar union with the first caudal. In this genus, as in all the Sau- 

 ropoda, each vertebra of the sacrum supports its own transverse proc- 

 esses. As shown in PI. XXIII, the articulation for the ilium is 

 formed by the coossification of the distal ends of the transverse 

 processes. The neural canal is much enlarged in the sacrum, but less 

 proportionally than in Stegosaurus. 



14 



15 



13 



Fig. 12 Sternal ribs of Brontomunre exceUus; outer view. 



Fig. 13. — The same specimen ; inner view. 



Fig. 14. — Sternal rib of same individual; outer view. 



Fig. 15 — The same rib ; inner view. 



All the figures are one-eighth natural size. 



THE CAUDAL VERTEBR.E. 



In the present species the three vertebrse next behind the sacrum 

 have moderate-sized cavities between the base of the neural arch and 

 the transverse processes. These shallow pockets extend into the base 

 of the processes, but the centra proper are solid. All the other cau- 

 dals have the centra, processes, and spines composed of dense bone. 

 The fourth caudal vertebra, represented in PI. XXIV, figs. 2 and 3, is 



