BONES OF THE FORE-ARM. 



47 



THE FORE-ARM. 



Describe the Ulna. The elbow-bone is the internal bone of the fore-arm. 

 It is larger and longer than the radius, forming the greater portion of the 

 articulation with the humerus. It does not enter into the formation of the 

 wrist-joint, being excluded therefrom by an interarticular fibro-cartilage. It 

 presents the following, viz. 



Olecranon Process^ at the upper extremity, forming the elbow. It is curved 

 forwards, its apex being received into the olecranon fossa of the humerus 

 when the fore arm is extended. Its posterior surface gives insertion to the 

 tendon of the triceps. In its function and structure it resembles the patella. 



Coronoid Process^ below the olecranon, projects forwards, its apex being 

 received into the coronoid fossa of the humerus when the fore-arm is 

 flexed. Its upper surface is concave for articulation with the humerus, 

 its lower surface rough for the insertion of the brachialis anticus muscle. 

 Its inner surface has a margin for the internal lateral ligament, a tubercle 

 for the flexor sublimis digitorum, and a ridge for the pronator radii teres. 



Greater Sigmoid Cavity / lies between the processes, and is divided by a 

 vertical ridge into two unequal parts. It articulates with the trochlear 

 surface of the humerus. 



Lesser Sigmoid Cavity c lies external to the coronoid 

 process ; is oval and concave, articulating with the 

 head of the radius, and giving attachment to the 

 orbicular ligament. 



Shaft," large and prismatic above, smaller and rounded 

 below, has the Nutrient Foramen J 'on its anterior sur- 

 face, and a prominent margins externally, to which 

 is attached the interosseous membrane. The shaft 

 gives attachment to 9 of the 12 muscles of the fore- 

 arm. 



Headh at the carpal end, articulates with the lesser 

 sigmoid cavity of the radius, and the fibro-cartilage 

 of the wrist-joint. 



Styloid Process j projecting from the head internally 

 and posteriorly, its apex gives attachment to the in- 

 ternal lateral ligament, and a depression at its root 

 to the fibro-cartilage of the joint. 



Groove, for the tendon of the extensor carpi ulnaris 

 muscle. 



FIG. 24. 



