576 MAMMALIAN ANATOMY 



Determination. When the ulna is held vertically, the olecranon 

 above and the sigmoid cavity toward the student, the coronoid process 

 is on the side to which the bone belongs. 



Articulation. The ulna articulates with the humerus, the radius, 

 the pisiform, and the cuneiform. 



Muscular Attachments. The following muscles are attached to 

 the ulna : 



To the upper extremity, on the anterior surface, the anconeus and 

 the inner humeral head of the triceps ; on the external surface, the 

 anconeus, the scapular and outer humeral heads of the triceps, the 

 extensor carpi ulnaris, and the extensor indicis; on the posterior 

 surface, the scapular head of the triceps ; on the internal surface, the 

 inner humeral and supracoudyloid heads of the triceps and the ulnar 

 heads of the flexor carpi ulnaris and flexor profundus digitorum ; 

 on the proximal surface, the posterior humeral and scapular heads of 

 the triceps. 



To the shaft, on the posterior surface, the extensor indicis and 

 extensor ossis metacarpi pollicis ; on the anterior surface, the radio- 

 ulnar head of the flexor profundus digitorum and the pronator 

 quadratus; on the internal surface, the brachialis anticus and the 

 ulnar head of the flexor profundus digitorum. 



Blood Supply. The nutrient artery of the ulna is derived from 

 the brachial artery, either directly or from its posterior interosseous 

 branch. 



Ossification. The ulna arises from three principal centres of 

 ossification, one for the shaft, one for the posterior end of the 

 olecranon, and one for the distal extremity. 



VARIATIONS IN THE ULNA. 

 VARIATIONS IN SIZE. 



The measurements of the ulna were taken as follows : 



The maximum length is the distance from the olecranon to the tip 

 of the styloid process. 



The width at the upper extremity is the distance from the superior 

 edge of the greater sigmoid cavity to the posterior surface. 



The width at the lower end is the distance from the most projecting 

 part of the superior edge of the facet for the ulna to the posterior 

 border, in the same direction as the preceding measurement. 



