218 



OSTEOLOGY 





ridge, which runs from the dorsal end of the radial notch, downward to the dorsal 

 border; the triangular surface above this ridge receives the insertion of the 

 Anconseus, while the upper part of the ridge affords attachment to the Supinator. 

 Below this the surface is subdivided by a longitudinal ridge, sometimes called the 

 perpendicular line, into two parts: the medial part is smooth, and covered by the 

 Extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from 

 above downward to the Supinator, the Abductor pollicis longus, the Extensor pollicis 

 longus, and the Extensor indicis proprius. 



The medial surface (fades medialis; internal surface) is broad and concave 

 above, narrow and convex below. Its upper three-fourths give origin to the 

 Flexor digitorum profundus; its lower fourth is subcutaneous. 



Olecranon 



Appears at __ 

 tenth year 



Appears 

 fourth year 



body at 

 sixteenth year 



Joins body at 

 twentieth year 



Inferior extremity 



Fia. 215. Plan of ossification of the ulna. 

 From three'centers. 



Fia. 216. Epiphysial lines of ulna in a young adult. 

 Lateral aspect. The lines of attachment of the articular 

 capsules are in blue. 



The Lower Extremity (distal extremity} .The lower extremity of the ulna is 

 small, and presents two eminences; the lateral and larger is a rounded, articular 

 eminence, termed the head of the ulna; the medial, narrower and more projecting, 

 is a non-articular eminence, the styloid process. The head presents an articular 

 surface, part of which, of an oval or semilunar form, is directed downward, and 

 articulates with the upper surface of the triangular articular disk which separates it 

 from the wrist-joint; the remaining portion, directed lateralward, is narrow, convex, 

 and received into the ulnar notch of the radius. The styloid process projects from 

 the medial and back part of the bone; it descends a little lower than the head, 

 and its rounded end affords attachment to the ulnar collateral ligament of the 

 wrist-joint. The head is separated from the styloid process by a depression for 

 the attachment of the apex of the triangular articular disk, and behind, by a shallow 

 groove for the tendon of the Extensor carpi ulnaris. 



