1-22 



THE SKELETON 



THE ULNA 



Tlie ulna is tlu- inner l)one uf the forearm: it lies parallel with, but is longer than, 

 the radius. The upper extremity is the thickest and strongest part of the ulna, 

 and is of irregular shape. The superior articular surface is called the greater 

 sigmoid cavity, and receives the trochlea of the humerus; it is transversely con- 

 stricted near its middle. The prominence above the constriction is termed the 

 olecranon, the part below the coronoid process. 



The olecranon process is the highest part of the ulna; into its upper surface 

 the triceps is inserted, antl the anterior margin of this surface affords attachment to 

 the po.steri()r ligament of the elbow. The anterior surface of the olecranon is 



Fig. 128. — Uppkk End of Left Ui.xa. (Outer view.) 



OLECRANON 

 GREATER SIGMOID FOSSA 



Orbicular ligament 



Oblique ligament 



Flexor profundus digitorum 



LESSER SIGMO'D FOSSA 



Supinator brevis 



Interosseous membrane 



articular, and forms the ui)per and back part of the greater sigmoid cavity, and its 

 margms give attachment to ligaments. The posterior surface of this process is 

 triangular, and separated from the skin merely by a bursa. On the inner side 

 there is a tubercle for the origin of ihe jiexor carpi ulnaris ; and below this a fasci- 

 culus of the internal lateral ligament of the ell>ow is inserted. The outer side 

 gives attachment to ])art of the anconeus. 



The coronoid process forms the lower lip of the greater sigmoid eavitv: its 

 upper sin-laee is aiti.ulnr and forms nearly a right angle with the olecranon portion. 

 The anterior edge of the coronoid jirocess is sometimes called the apex The 

 inferior aspect is rough for the insertion of the hmchialis anticus muscle and the 

 lower outer angle has a tub.-rcle to which the ol)lique ligament is attached The 

 inner edge has a smooth tul)ercle from which the flexor mblimis diqitorvm arises- 

 the ridge of bone immediately below this tubercle gives origin to the lesser head of 

 ihc pronator radn teres, and below this again the rounded accessory l)undle of the 

 flexor longiis polhcin arises. 



