Olecranon 



OSTEOLOGY 



The Ulna (Elbow Bone). 1 



The ulna (Figs. 212, 213) is a long bone, prismatic in form, placed at the medial 

 side of the forearm, parallel with the radius. It is divisible into a body and 

 two extremities. Its upper extremity, of great thickness and strength, forms 

 a large part of the elbow-joint; the bone diminishes in size from above downward, 



its lower extremity being very small, and excluded 

 from the wrist-joint by the interposition of an 

 articular disk. 



The Upper Extremity (proximal extremity) (Fig. 

 212). The upper extremity presents two curved 

 processes, the olecranon and the coronoid process; 

 and two concave, articular cavities, the semilunar 

 and radial notches. 



The Olecranon (olecranon process). The olecra- 

 non is a large, thick, curved eminence, situated 

 at the upper and back part of the ulna. It is bent 

 forward at the summit so as to present a promi- 

 nent lip which is received into the olecranon fossa 

 of the humerus in extension of the forearm. Its 

 base is contracted where it joins the body and the 

 narrowest part of the upper end of the ulna. Its 

 posterior surface, directed backward, is triangular, 

 smooth, subcutaneous, and covered by a bursa. 

 Its superior surface is of quadrilateral form, marked 

 behind by a rough impression for the insertion of 

 the Triceps brachii; and in front, near the margin, 

 by a slight transverse groove for the attachment 

 of part of the posterior ligament of the elbow-joint. 

 Its anterior surface is smooth, concave, and forms 

 the upper part of the semilunar notch. Its borders 

 present continuations of the groove on the margin 

 of the superior surface ; they serve for the attach- 

 ment of ligaments, viz., the back part of the ulnar 

 collateral ligament medially, and the posterior 

 ligament laterally. From the medial border a part 

 of the Flexor carpi ulnaris arises; while to the 

 lateral border the Anconaeus is attached. 



The Coronoid Process (processus coronoideus) . 

 The coronoid process is a triangular eminence 

 projecting forward from the upper and front part 

 of the ulna. Its base is continuous with the body 

 of the bone, and of considerable strength. Its 

 apex is pointed, slightly curved upward, and in 

 flexion of the forearm is received into the coronoid 



fossa of the humerus. Its upper surface is smooth, concave, and forms the lower 

 part of the semilunar notch. Its antero-inferior surface is concave, and marked by 

 a rough impression for the insertion of the Brachialis. At the junction of this 

 surface with the front of the body is a rough eminence, the tuberosity of the ulna, 

 which gives insertion to a part of the Brachialis; to the lateral border of this 

 tuberosity the oblique cord is attached. Its lateral surface presents a narrow, 

 oblong, articular depression, the radial notch. Its medial surface, by its prominent, 



FIG. 212. Upper extremity of left ulna. 

 Lateral aspect. 



1 In the anatomical position, the forearm is placed in extension and supination with the palm looking forward 

 and the thumb on the outer side. 



