146 THE DESEADO FORMATION OF PATAGONIA 



is only large enough to actually eover about half of the head 

 of the humerus, and fits so that, in a position of rest, the 

 glenoid covered the outer part of the humeral head, and 

 only articulated on the inner part of the humerus head 

 when the limb was bent inward. The blade of the scapula 

 is narrow, with the proximal end prolonged and ending 

 in a thick rugose mass. The anterior and posterior mar- 

 gins are rugose and thickened, the great thickness of the 

 proximal end being due to the convergence of these thick- 

 ened margins and the heavy spine. Lastly, this thick 

 proximal end is peculiar in having on its posterior side a 

 large rugose cavity, which was apparently to receive mus- 

 cular attachments. 



For such a heavy animal, the humerus is extraordinarily 

 long and slender. The sessile head is strongly compressed 

 from side to side, very convex, and much larger than the 

 glenoid fossa, its articular surface extending onto the base 

 of the greater tuberosity. This tuberosity is heavy and 

 thick, but does not project above the head. The powerful 

 deltoid ridge extends from the tuberosity two-thirds of 

 the way down the shaft. The shaft is unusually slender. 

 Distally it expands laterally to make the two large epicon- 

 dyles, of nearly equal size. The trochlca is relatively 

 narrow, the internal surface being the narrower, and rising 

 to a high margin; while the external portion is wider, 

 rounded, and has a low margin. The supratrochlear 

 fossa is moderately deep, the anconeal fossa somewhat 

 deeper, but there is no connecting foramen. 



Gaudry* figures a radius and ulna, both relatively long 

 bones, and closely apposed; so that there was no possibility 

 of a rotary motion of the forearm. The proximal end 

 of the radius is expanded, so that its articular surface 

 is in contact with the full width of the humeral trochlea 

 on the anterior side. Below, the bone contracts to a 

 moderately slender shaft, and then expands distally into 



*Anal. Palacontologic, t. I, p. 5, 1906. 



