The ulna presents at its superior extremity a posterior process, the olecranon, which forms the point of the elbow. We find on the anterior surface of the same, another process, the coronoid.
Fig. 25.—Superior Extremity of the Bones of the Human Forearm: Left Side, Superior Surface.
1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.
Fig. 26.—Superior Extremity of the Bones of the Forearm of the Dog: Left Limb, Superior Surface.
1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.
It is necessary to dwell on the relations of these parts. In man the head of the radius is situated at the anterior part of the external surface of the superior extremity of the ulna ([Fig. 25]); indeed, the small sigmoid cavity with which the head articulates is situated on the outer side of the coronoid process, and this apophysis is placed in front. In the plantigrades and digitigrades the head of the radius is placed still more forward, so much so that it is situated almost in front of the superior extremity of the ulna ([Fig. 26]). In the unguligrades it is placed directly in front of this latter ([Fig. 27]).