

THE ULNA 



215 



free margin, serves for the attachment of part of the ulnar collateral ligament. 

 At the front part of this surface is a small rounded eminence for the origin 

 of one head of the Flexor digitorum sublimis; behind the eminence is a depression 

 for part of the origin of the Flexor digitorum profundus; descending from the 

 eminence is a ridge which gives origin to one head of the Pronator teres. Fre- 

 quently, the Flexor pollicis longus arises from the lower part of the coronoid 

 process by a rounded bundle of muscular fibers. 



The Serailunar Notch (indsura semilunaris; greater sigmoid cavity). The semi- 

 lunar notch is a large depression, formed by the olecranon and the coronoid process, 

 and serving for articulation with the trochlea of the humerus. About the middle 

 of either side of this notch is an indentation, which contracts it somewhat, and 

 indicates the junction of the olecranon and the coronoid process. The notch is 

 concave from above downward, and divided into a medial and a lateral portion by 

 a smooth ridge running from the summit of the olecranon to the tip of the coronoid 

 process. The medial portion is the larger, and is slightly concave transversely; 

 the lateral is convex above, slightly concave below. 



The Radial Notch (indsura radialis; lesser sigmoid cavity). The radial notch 

 is a narrow, oblong, articular depression on the lateral side of the coronoid process ; 

 it receives the circumferential articular surface of the head of the radius. It is 

 concave from before backward, and its prominent extremities serve for the attach- 

 ment of the annular ligament. 



The Body or Shaft (corpus ulnce). The body at its upper part is prismatic 

 in form, and curved so as to be convex behind and lateral ward; its central part 

 is straight; its lower part is rounded, smooth, and bent a little lateralward. It 

 tapers gradually from above downward, and has three borders and three surfaces. 



Borders. The volar border (margo volaris; anterior border) begins above at the 

 prominent medial angle of the coronoid process, and ends below in front of the 

 styloid process. Its upper part, well-defined, and its middle portion, smooth and 

 rounded, give origin to the Flexor digitorum profundus; its lower fourth serves 

 'or the origin of the Pronator quadratus. This border separates the volar from 

 the medial surface. 



The dorsal border (margo dorsalis; posterior border) begins above at the apex of 



e triangular subcutaneous surface at the back part of the olecranon, and ends 

 oelow at the back of the styloid process; it is well-marked in the upper three- 

 tourths, and gives attachment to an aponeurosis which affords a common origin to 

 the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor digitorum pro- 

 fundus; its lower fourth is smooth and rounded. This border separates the medial 

 from the dorsal surface. 



The interosseous crest (crista interossea; external or interosseous border) begins 

 above by the union of two lines, which converge from the extremities of the radial 

 notch and enclose between .them a triangular space for the origin of part of the 

 Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower 

 fourth smooth and rounded. This crest gives attachment to the interosseous mem- 

 brane, and separates the volar from the dorsal surface. 



Surfaces. 1 The volar surface (fades volaris; anterior surface), much broader 

 above than below, is concave in its upper three-fourths, and gives origin to the 

 Flexor digitorum profundus; its lower fourth, also concave, is covered by the 

 Pronator quadratus. The lower fourth is separated from the remaining portion 

 by a ridge, directed obliquely downward and medialward, which marks the extent 

 of origin of the Pronator quadratus. At the junction of the upper with the 

 middle third of the bone is the nutrient canal, directed obliquely upward. 



The dorsal surface (fades dorsalis; posterior surface) directed backward and 

 lateralward, is broad and concave above; convex and somewhat narrower in the 

 middle; narrow, smooth, and rounded below. On its upper part is an oblique 



