THE OSTEOLOGY OF THE DIADECTIDAE 149 



in the seventh presacral. The last two vertebrae have the trans- 

 verse processes much smaller than the preceding ones, and the upper 

 end is much farther to the rear; the articular face is more nearly 

 horizontal. The articular faces for the ribs are very poorly devel- 

 oped, in strong contrast with the condition of the more anterior ver- 

 tebras; these two may be recognized as lumbars. 



The two sacrals present a strong contrast to the presacrals. They 

 are closely anchylosed together, so that not only are the centra joined, 



Fig. 16. — Outline of vertebrae shown in Fig. 15. One-half natural size. 



but the zygapophysial articulations have disappeared and the pro- 

 cesses pass into one another without suture. Both vertebrae present 

 well- developed articular zygapophysial faces to the adjacent lumbar 

 and caudal vertebrae. The transverse process of the first sacral is 

 very wide, originating from the bases of the zygapophysial pro- 

 cesses and maintaining a width equal to the anterior-posterior diame- 

 ter of the centrum. The articular face for the rib is completely 

 horizontal, but the rib is anchylosed to the process, so the face is 

 traceable by a suture line only. The process and rib extend almost 

 straight downward and articulate with the anterior end of the ilium 

 (shown by specimen No. 1075). The transverse process of the 

 second sacral is very much narrower and more rounded than the 

 first, but extends downward, and is anchylosed with a sacral rib as 

 in the first. The neural spine of the first sacral is larger than the 



