or horned Dinosaurs, of North America. 173 



of the ribs, as in Crocodiles, a feature not before seen in 

 Dinosaurs (Plate III, figures 5-6). 



The Sacrum. 



The sacrum was strengthened by union of several vertebrae, 

 ten being coossified in one specimen of Triceratops (Plate IV). 

 The middle or true sacral vertebrae have double transverse 

 processes, diapophyses being present, and aiding in supporting 

 the ilium. This character has been seen hitherto, in the 

 Dinosauria, only in Ceratosaurus and some other Theropoda. 



The main support of the pelvis was borne by four vertebrae, 

 which evidently constituted the original sacrum. In front of 

 these, two others have only simple processes, and apparently 

 were once dorsals or lumbars. Three vertebrae next behind 

 the true sacrum have also single processes, and the fourth, or 

 last of the series, has the rib process weak, and not reaching 

 the ilium (Plate IV). Seen from the side, the sacrum is much 

 arched upward, and the neural spines of the true sacrum are 

 firmly coossified. In the median region, the sacral vertebrae 

 have their centra much compressed, but the last of the series 

 are widely expanded transversely. The whole appearance of 

 the sacrum is remarkably avian. The neural canal of the 

 sacral vertebrae has no special enlargement, thus differing 

 widely from that in Stegosaurus. 



The Caudal Vertebrae. 



The caudal vertebrae are short, and the tail was of moderate 

 length. The first caudal has the anterior face of the centrum 

 concave vertically, but flat transversely, and a short, massive 

 neural spine with expanded summit (Plate V, figures 1-3). 

 In the median caudals, the centra have biconcave articular faces, 

 and weak neural spines. The distal caudals are longer than 

 wide, with the ends nearly round, and concave. 



The Scapular Arch and Fore Limbs. 



The scapula is massive, especially below. The shaft is long 

 and narrow, with a thin edge in front, and a thick posterior 

 margin above the glenoid fossa. The distal portion has a 

 median external ridge, and a thick end (Plate VI, figure 1, so). 



The coracoid is rather small, and in old individuals may 

 become united to the scapula. It is sub rhombic in outline, and 

 is perforated by a large and well-defined foramen. No indica- 

 tions of a sternum have yet been found in this group. 



The humerus is large and robust, and similar in form to that 

 of Stegosaurus. It is nearly as long as the femur in one 



