26 
PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
border is also convex centrally, but immediately above the glenoid fossa 
and below the inferior angle it is concave. A high narrow spine is present, 
terminating in a slender acromion process and supporting a large met- 
acromion, the distal portion of which has not been preserved. The body 
of the bone is very thin and has been slightly deformed by crushing, pro- 
ducing an undulatory surface throughout the floor of the supraspinous 
fossa. The infraspinous fossa is triangular in outline and deeply concave 
transversely. The glenoid surface (PI. IV, fig. 11) is continued forward 
to the extremity of the large bicipital tubercle. Apart from this prolong- 
ation, the outline of the glenoid fossa is approximately circular. The 
margins are but little elevated. The fossa is slightly concave in all 
diameters. The coracoid process is short, with its free margins curved 
inward. 
The proximal extremity of the humerus (Pis. IV, figs. 6, 7 ; VI, fig. 1) is 
the stoutest and heaviest portion of that bone. The head, which is hemi- 
spherical in shape, projects a considerable distance beyond the posterior 
margin of the shaft. The tuberosities are low, the greater tuberosity 
rising but little above the level of the head. It is separated from the 
lesser tuberosity by a broad bicipital groove. Antero-externally, the 
proximal surface of the shaft is flattened, supporting a broad triangular 
area, the apex of which is continued distally as the deltoid ridge. Some 
distance above the distal extremity of the deltoid ridge, on the inner 
surface of the shaft, is a prominent rugosity for muscular attachment, 
corresponding in position to the area of insertion of the coracobrachial 
muscle in the rabbit. The shaft is slightly curved antero-posteriorly and 
somewhat flattened laterally. The distal end is expanded transversely. 
The supinator ridge is very slightly developed, but the inner epicondyle 
is prominent and a large internal epicondylar foramen is present. The 
distal articular surface is characterized by the great prominence of the 
inner lip of the trochlea and the absence of any sharp demarcation be- 
tween the latter and the capitellum. Posteriorly, both lips of the trochlea 
are sharp (PI. IV, fig. 7), the inner exceeding the outer in elevation, but 
farther forward the outer lip terminates suddenly at the margin of the 
capitellar expansion (PI. IV, fig. 6). No perforation unites the anconeal 
and coronoid fossae. 
The radius (Pis. IV, figs. 12-14; VI, fig. 2) is strongly curved antero- 
posteriorly. The shaft is elliptical in cross-section proximally, but dis- 
