172 THE DESEADO FORMATION OF PATAGONIA 
The humerus is a very characteristic bone, short and 
stout, but greatly flattened from front to back. It has 
a large sessile head, which is strongly convex, and projects 
internally over the margin of the shaft. The external 
tuberosity is large and rugose but does not project above 
the level of the head. The deltoid ridge is shifted to the 
external side of the bone, and makes a long, muscular 
ridge, while on the opposite external margin is a second 
ridge, and between the first and second ridges a long furrow 
or trough is inclosed. These terminate just below the 
middle of the bone in roughened bosses, which all but meet. 
The epicondyles are large and give the excessive width 
to the bone. The external condyle is prolonged upward 
and ends in a spur. The trochlea is of moderate width 
and gently undulated. The supratrochear fossa is only 
slightly depressed, and the anconeal fossa is likewise 
shallow. The bone has no exact counterpart, but is simi- 
lar to that of Moeritherium and Palaeomastodon, but in 
each case is more flattened and has the external ridges more 
developed. 
Gaudry describes the radius and ulna. They are 
ridiculously short, and very massive. The ulna is stout 
with a massive olecranon which is directed well toward the 
rear. The sigmoid notch is shallow, the coronoid process 
short, and the articular area expanded so that the ulna 
covers the whole of the posterior of the trochlea of the 
humerus. The upper end of the radius is compressed 
antero-posteriorly, but distally it expands into a heavy 
bone. Its upper articulation is expanded, so that it comes 
in contact with the full width of the anterior portion of 
the trochlea of the humerus. 
The carpus and front foot are of questionable associa- 
tion. Ameghino described a front foot as P. romeri, and 
later Tournouer assigned this foot to Astrapotheriwm. 
However, I have seen no reason to think it belongs to 
Astrapotherium, being far too small, and.so would for 
