ULNA, RADIUS 



57 



FOREARM, OR ANTEBRACHIUM 



Ulna. A long bone in structure and form, situated in the 

 medial side of the forearm (the ulnar side). The upper extremity 

 presents two strongly marked processes the olecranon, pro- 

 jecting upward from the back and curving 

 forward, and the coronoid, projecting forward 

 from, the front and curving upward. Thus 

 these processes curve toward each other, and 

 the cavity between them is the semilunar 

 notch. It receives the trochlea of the humerus 

 to form the elbow-joint. On the lateral side 

 of the coronoid process is the radial notch, 

 where the head of the radius lies. 



The lower extremity is the head of the 

 ulna, which lies in the ulnar notch of the ra- 

 dius. There is a well-marked projection on 

 this head called the styloid process. 



The posterior border of the shaft is subcutaneous 

 and may be traced down from the point of the elbow. 

 The space between the radius and the ulna is called 

 the interosseous space, and is occupied by an interos- 

 seous membrane. 



Radius. A long bone in structure and in 

 form, situated on the lateral side of the forearm 

 (the radial side). 



The upper (or proximal) extremity is the 

 head, which is depressed at the top to fit the 

 capitulum of the humerus. Below the head is 

 the neck, and below that, in front, is the 

 tuberosity of the radius for the attachment of 

 the biceps muscle of the arm. The lower (or 

 distal) extremity of the radius is broad and 

 thick, and is the largest bone in the formation 

 of the wrist-joint. 



On its lateral aspect is the styloid process. Run- 

 ning across the upper half of its anterior surface is 

 the oblique line, which is a part of the anterior border. 



Special notes. The head of the humerus is proximal and articulates with 



FIG. 52. LEFT 

 ULNA AND RADIUS, 

 ANTERIOR SUR- 

 FACES. (Sappey.) 



i, Shaft or body 

 of ulna; 2, semilunar 

 notch; 3, radial 

 notch occupied by 

 radial head; 4, olec- 

 ranon; 5, coronoid 

 process; 6, orifice 

 for nutrient artery; 



7, interosseous bor- 

 ders with interos- 

 seous space between; 



8, head of ulna; 9, 

 styloid process of 

 ulna; 10, shaft or 

 body of radius; n, 

 12, head and neck 

 of radius; 13, tu- 

 berosity of radius; 

 14, marking for mus- 

 cle; 15, 16, lower ex- 

 tremity and styloid 

 process. 



