592 



MAMMALIAN ANATOMY 



FIG. 452. 



line at the upper limit of the area of attachment of the pronator quad- 

 ratus muscle. 



The posterior border may be absent, in which case it is represented 

 by the maximum convexity of the posterior aspect of the bone. 



HUMAN RADIUS. 



The radius of man differs from the radius of the cat (Fig. 453) in a 

 few details only. The proximal surface of the head is almost circular ; 



the marginal surface presents a more extensive 

 articular band, because the radius can rotate 

 more completely around its long axis, bring- 

 ing the lower end parallel with the ulna and 

 placing the hand in absolute supination, which 

 the radius of the cat cannot do. The head and 

 neck are not bent so strongly outward from the 

 axis of the shaft. 



The tubercle is marked more deeply by 

 the insertion of the biceps muscle. 



The shaft presents the same anterior, in- 

 ternal, and posterior borders, likewise sepa- 

 rating anterior, posterior, and external sur- 

 faces. Some authors give only two borders, 

 the inner and the outer, and two surfaces, the 

 anterior and posterior ; in this case the outer 

 border is equivalent to the anterior border and 

 external surface, and the posterior border is 

 not distinguished from the general posterior 

 surface. 



The internal or interosseous border is 

 distinct, and separates the anterior and poste- 

 rior surfaces. The upper part of the anterior 

 border is formed by the oblique line, and there- 

 fore begins at the tubercle, and not at the outer 

 side of the head. The area above the line for 



the supinator brevis muscle, which in the cat I have called part of 

 the anterior surface, is in man rounded and faces outward as part of the 

 external surface. The area of attachment of the pronator quadratus 

 on the lower part of the anterior surface is less extensive in man than 



BONES OF THE RIGHT FORE- 

 ARM. VIEWED IN FRONT; 

 THE ULNA TO THE RIGHT 

 AND THE RADIUS TO THE 

 LEFT OF THE FIGURE. 



1, shaft of the ulna; 2, greater 

 sigmoid cavity ; 3, articulation of 

 the head of the radius with the 

 ulna ; 4, olecranon ; 5, coronoid 

 process; 6, nutrient foramen; 7, 

 sharp ridges of both bones of the 

 forearm for the attachment of the 

 interosseous membrane ; 8, head 

 of the ulna; 9, styloid process; 

 10, shaft of the radius; 11, head of 

 the same; 12, neck ; 13, tuberosity ; 

 14, roughened attachment of the 

 pronator radii teres muscle; 15, 

 distal extremity of the bone; Iti, 

 its styloid process. 



