578 



MAMMALIAN ANATOMY 



FIG. 444. 



HUMAN ULNA. 



The ulna of man is relatively shorter and stouter than the ulna 

 of the cat. The upper end is bent forward and inward. 



The greater sigmoid cavity is at the upper limit of the proximal 

 extremity, hence its upper edge is also the anterior superior edge of 



the olecranon. The sigmoid cavity is almost 

 as broad as it is long, and it is more deeply 

 concave. The olecrauon part is separated from 

 the lower part by a distinct ridge. 



The coronoid process has a thin edge facing 

 upward, and is not a pyramidal process sloping 

 downward, as in the cat. Its roughened anterior 

 surface, sometimes called the tuberosity of the 

 ulna, is an area of insertion of the brachialis 

 anticus muscle ; to a tubercle at its lower outer 

 angle is fastened the oblique ligament ; on its 

 inner edge is a smooth tubercle for the attach- 

 ment of the flexor sublimis digitorum muscle. 



The lesser sigmoid cavity is not so deeply 

 concave nor so regular as that cavity in the 

 cat's ulna. The upper surface of the olecranon 

 is not transversely concave ; it forms an obtuse 

 rounded angle with the posterior surface. 



The shaft presents three borders, internal, 

 external, and posterior, separating three sur- 

 faces, anterior, internal, and posterior. 



The internal border begins above, at the 

 inner side of the coronoid process, as a sharp 

 ridge for the pronator radii teres and flexor 

 longus pollicis muscles, and continues down to 

 the styloid process. It is rounded for most of 



its extent, and affords attachment to the flexor profundus digitorum 

 muscle. To the lower and sharper part is fastened the pronator 

 quadratus. In its upper third is the nutrient foramen of the bone. 



The external border stretches from the back of the lower sigmoid 

 cavity to the anterior side of the head. For most of its extent it 

 is a sharp interosseous border for the attachment of the interosseous 

 membrane. It separates the anterior and posterior surfaces. 



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; 16, 

 its styloid process. 



