98 THE ROYAL SOCIETY OF CANADA 



thickened and rugose border. Both the external and internal faces 

 of the shaft are fiat near the proximal end, but the median external 

 portion is gently rounded dorso-ventrally, while internally it is 

 concave in the same direction. 



About three-fifths of the distance from the proximal end the 

 superior border of the shaft diverges, forming a prominent ridge on 

 the external surface for about 130 mm, and terminates in a well- 

 developed acromion process (Plate II, Fig. la. p.) which points obliquely 

 outward. The presence of an acromion process is a marked point of 

 difference from Ankylosaurus^^ and Stegosaiirus^^ . This ridge is, 

 doubtless, homologous with the spine of the mammalian scapula 

 though it does not divide the upper half of the scapula nor does it 

 reach the distal end of that bone. 



Directly below the acromion process there is a large rugose area 

 which probably served for the attachment of the deltoid muscles 

 (Plate II, Figure 1). 



At the point where the superior border begins to diverge the edge 

 is thickened and slightly flattened toward the inner side. From this 

 point the internal superior border starts at a lower level than does 

 the outer border and ascends very rapidly to its highest point, which 

 is near its union with the coracoid. At the distal end the scapula is 

 very broad and massive. Its thickness in the glenoid cavity is 

 85 mm. 



The glenoid cavity is large and is an almost perfect semicircle in 

 outline measuring 110 mm. from lip to lip of the external border. 

 The scapula does not contribute as much to its formation as does the 

 coracoid. 



Length of scapula 410 mm. 



Greatest breadth of scapula (just above glenoid cavity) 195 " 



The coracoid is large and massive. In outline it more nearly 

 approaches the coracoid of Triceratops than that of Stegosaurus though 

 the anterior portion is longer than in Triceratops and not so high. 

 The superior border is relatively thin and the inner face is concave. 

 The external surface is moderately flat except the proximal inferior 

 portion, which is greatly thickened to contribute to the formation of 

 the glenoid cavity. The inferior border is thick and the anterior end 

 is thickened and roughened for the attachment of ligaments. 



The coracoid foramen (Plate II, Figure 1) is large and elliptical 

 and runs from the external surface diagonally backward emerging on 



12 Bull. Amer. Museum of Nat. Hist., vol. XXXVH, 1917, p. 196. 

 " U.S. Nat. Mus. Bull. 89, 1914, p. 67. 



