THE ULNA. 



211 



OLECRANON 



INCISURA SEMILUNARI 



CORONOID PROCESS 



INTEROSSEOUS 



CREST 



longus muscles, from above downwards. The smooth medial surface of the 

 coronoid process merges with the olecranon dorsally, and with the medial surface 

 of the body distally. 



The incisura semihmaris (O.T. 

 greater sigmoid cavity), for articulation 

 with the trochlea of the humerus, is a 

 semicircular notch, the proximal part of 

 which is formed by the volar surface of 

 the olecranon, whilst distally it is com- 

 pleted by the proximal surface of the 

 coronoid process. Constricted towards 

 ,its deepest part by the notching of 

 its borders, the articular surface is 

 occasionally crossed by a narrow im- 

 pression which serves to define the ole- 

 cranon proximally from the coronoid 

 distally. The articular area is divided 

 'into a medial portion, slightly con- 

 cave transversely, and a lateral part, 

 transversely convex to a slight degree, 

 : by a longitudinal smooth ridge which 

 3xtends from the most prominent part 

 of -the border of the olecranon proxirn- 

 illy to the most outstanding point 

 'of the coronoid process distally. The 

 margins of the semilunar notch are 

 sharp and well defined, and serve, with 

 the exception of the area occupied by 

 the radial notch, for the attachment of 

 the capsule of the elbow-joint. 



The radial notch(O.T. lesser sigmoid 

 cavity), placed on the radial side of 

 'the coronoid process, is an oblong 

 irticular surface for the reception of 

 'she head of the radius. It encroaches 

 bn the distal and lateral part of the 

 sernilunar notch, so as to narrow it 

 Considerably. Separated from it by 

 i rectangular curved edge, it displays 

 i surface which is plane proximo- 

 listally, and concave from before 

 Backwards. .Its volar extremity is 

 larrower and more pointed than its 

 'lorsal, and becomes confluent with 

 : /he anterior edge of the coronoid pro- 

 jess, at which point the annular liga- 

 nent, which retains the head of the 

 'adius in position, is attached in front. 

 .ts dorsal border, wider and more out- 

 Standing, lies in line, and is continuous 

 ivith the interosseous margin of the 

 'haft. Dorsal to this border, the annu- 

 ar ligament is attached posteriorly. 



The body of the ulna (corpus ulnae), 

 ;rtiich is nearly straight, or but slightly 

 urved, is stout and thick proximally, 

 :;radually tapering towards its distal extremity. It may be divided into three 

 irfaces, a volar (O.T. anterior), a dorsal or posterior, and a medial, by three 

 veil -defined borders, an interosseous crest, a dorsal margin, which latter is 



TUBEROSITY 



BlCIPITAL HOLLOW 



INTEROSSEOUS 



BORDER 



OR CREST" 



HEAD 



STYLOID 

 PROCESS 



FIG. 203. THE RIGHT RADIUS AND ULNA SEEN 

 FROM THE VOLAR ASPECT. 



