614 GEOLOGICAL SURVEY OF THE TERRITORIES. 
condition of the proximal extremity. It presents, for examination, the 
articular facets for the ginglymoid joint it forms with radius and ulna, 
and the superior and inferior condyles. The larger, and at the same 
time the superior, of these two facets is intended for the cup-shaped 
depression in the head of the radius, as well as a portion of the articu- 
lar surface on the ulna. Itis ovoid in form and placed obliquely on the 
bone, the inferior end of the long axis of the oval being situated the 
nearer the proximal extremity of the shaft. This facet is separated 
from the trochlea surface for the ulna by a well-marked depression; this 
latter is a knob-like tubercle when compared with. the radial facet. 
The condyles and the entire articular surface are about in the same 
plane posteriorly ; that is, neither increases the length of the bone, 
one more than another. Passing from the trochlear surface for the 
ulna towards the inner aspect of the shaft, there is to be observed 
a shallow depression, which corresponds to the olecranon fossa of 
human osteology, and in full extension of the limb allows room for 
that process of the ulna in this bird. The radius has an average length 
of 6.6 centimetres, and the ulna a corresponding length of 6.8 centi- 
metres, so that their distal extremities, when articulated, as we exam- 
ine them in the closed wing, extend beyond the head of the humerus. 
In this position also the radius occupies a higher level than the ulna, 
and is the innermost bone of the two. The radius is slender, the trans- 
verse diameters of its subcylindrical shaft varying but little throughout 
its extent, though its extremities areexpanded. From the elbow-joint, 
when the two bones are in position, it at first diverges from the ulna at 
a moderate curve, to approach that bone again by a more gentle incli- 
nation to nearly absolute contact at the junction of middle and distal 
thirds ; from this latter point it lies parallel with the ulna to the wrist. 
The head of the radius is elliptical, being crowned by a depression for 
articulation with the oblique faceé on the distal end of the humernus. 
Beyond, below, and to the outer aspect of this facet is another of similar 
form, though convex for articulation with the ulna, while still more ad- 
vanced toward the distal end we find the bicipital tuberosity, and still 
more distally, the minute nutrient foramen ; all of the bones beyond the 
humerus being non-pneumatic. The distal extremity of the bone in 
question is terminated by a little fan-like expansion that caps the ulna 
and articulates by its anterior convex margin with the scapho-lunar of 
the wrist. It is marked above by the longitudinal groove for the tendon 
of the extensor metacarpi radialis longus. The shaft of the ulna is 
nearly three times as large as that of the radius. Its outer half is 
straight, its inner curved towards the humerus, thereby increasing, at 
the proximal moiety, the interosseous space, by the assistance of the 
opposite curve made by the radius. The stronger end is the one in- 
volved in the formation of the elbow-joint; here is to be observed 
the depression for the head of the radius, or the lesser sigmoid cavity, 
while the articular surface beyond that occupies the entire end of the 
bone, directed downwards, inwards, and backwards, presents for exam- 
ination the greater sigmoid cavity, the olecranon and coranoid processes, 
and the cavity for articulation with the oblique facet of the humerus. 
The greater sigmoid cavity is subcircular and of some depth; its lower 
and produced lip represents the coranoid process, as does its upper, 
better marked, aud more tuberous prolongation represent the olecranon 
of andranatomia. Extending radiad is another concave, quadrate, ar- 
_ ticular facet for the oblique tubercle of the humerus, as the first-men- 
tioned concavity articulates with the ulnar tubercle or trochlea. A 
little beyond this articular surface are various small tuberosities and 
eo = Sa 
