THE SCAPULA 51 



figured by Hatcher. 21 There, the fusion is complete although the suture is still visible. The form 

 01 both coracoids and scapulae in the two species is very similar and the size approximately the same. 

 The external surface of the coracoid is somewhat coin ex except toward the scapular surface and 

 that of the glenoid fossa, where the bone thickens rapidly and as a consequence becomes concave. 

 The internal surface is concave throughout. The outline agrees with that of M. crassus, having the 

 same posterior hook-like process. Hatcher describes the coracoid foramen as midway between the 

 anterior and posterior borders, directly opposite the point where the coraco-scapular suture joins the 

 glenoid surface. Internally, the foramen opens at the coraco-scapular suture. Externally, the 

 coracoid of the Yale specimen agrees; internally, however, the right coracoid (restored) shows the 

 foramen about 20 mm. away from the suture. The left coracoid is more in agreement and is probably 

 the more correct. There is no essential disagreement with Centrosaurus nasicornus. 



Scapula 



(Fig. 19) 



The scapulae agree with Hatcher's description of M. crassus. The external surface is convex 

 longitudinally, although tending to straighten toward the distal end. The inner surface, concave 

 longitudinally, is deeply so transversely, especially at the proximal third. Hatcher says that the 

 coraco-scapular suture just about bisects the glenoid fossa; with our specimen the greater part of 

 the fossa is formed by the scapula, the lesser by the coracoid. The scapula dilates at the fossa, and 

 is heavy at the proximal end, thinning out at the distal end of the blade. There is in each case a 

 slightly rugose area just above the glenoid fossa from which a low (Hatcher says prominent 22 ) 

 ridge extends obliquely outward toward the anterior edge at the distal end. In Triceratops, this 

 ridge arises in the same manner, but curves at about one-third of its length in such a way that it 

 terminates at the middle of the distal end of the blade instead of toward its anterior edge. The 

 scapula of the contemporary Chasmosaurus agrees with that of Centrosaurus in this respect, whereas 

 the ridge in the Edmonton genus Anchiceratops does not reach the anterior border and tends toward 

 the condition found in Triceratops, thus showing an evolutionary trend. 



Dimensions 



Coracoid C. flexus Y.P.M. M. crassus 



Antero-posterior diameter 365 mm. 336 mm. 



Transverse diameter 217 176 



Coraco-scapula 



Over-all length 810 840 



Sternum 



Additional morphological data concerning Triceratops, learned since the writing of the Cera- 

 topsia Monograph, include but three items, the sternal plates, a hyoid element and the complete 

 pes. The first were actually made known before the publication of the Monograph but the descrip- 

 tion of them was not included. Our knowledge of these elements is based upon the discovery of a 

 very imperfect Triceratops skeleton, without skull, found by the American Museum of Natural 

 History expedition of 1902 in the Hell Creek region of Montana, about a mile from the locality 

 of the T. serratus skull (No. 970 A.M.N.H.) described by the author 23 in 1903. 



21 Hatcher, Marsh, Lull, 1907, Fig. 84. 



22 Hatcher, Marsh, Lull, 1907, p. 79. 



23 Lull, R. S., 1903. 



