THE BONES OF THE UPPER LIMB 197 



The Ulna. 



The ulna is the internal bone of the forearm (which is assumed 

 to be in a position of supination). It is parallel with, and longer 

 than, the radius, and extends from the elbow to the WTist, being 

 separated from the latter joint by the triangular interarticular 

 fibro-cartilage. It is a long bone, and is divisible into a shaft and 

 two extremities, the upper of which is of large size. 



The upper extremity presents the olecranon and coronoid processes, 

 and the great and smaU sigmoid cavities. The olecranon process 

 forms the highest part of the bone, and is curved forwards at its upper 

 part. It is largely subcutaneous. Superiorly it presents a broad, flat, 

 quadrilateral surface, at the back part of which is a rough elevation 

 for the insertion of the triceps. In front of this there is a smooth 

 area where a bursa intervenes between that muscle and the bone. 

 At its anterior part, near the anterior margin, there is a narrow 

 transverse impression f(3r part of the posterior hgament of the 

 elbow-joint. The superior surface is limited anteriorly by a 

 sharp convex border, projected at its centre into a process, called 

 the beak, which overhangs the upper part of the great sigmoid 

 cavity, and is received into the olecranon fossa of the humerus 

 in extension of the joint. The anterior surface is directed down- 

 wards and forwards, and forms the upper part of the great sigmoid 

 cavity. The posterior surface, smooth, flat, and triangular, is 

 subcutaneous, and covered by a bursa. The inner surface pre- 

 sents a tubercle for the ulnar head of the flexor carpi ulnaris, and 

 the inner border gives attachment to the posterior part of the 

 internal lateral ligament of the elbow- joint. The outer surface 

 gives insertion to a portion of the anconeus, and the outer border 

 gives attacb_ment to fibres of the posterior hgament of the joint. 



The coronoid process is triangular, and projects forwards. The 



superior surface forms the lower and anterior part of the great 



sigmoid cavity. The inferior surface is rough and concave, and the 



roughness is prolonged upon the anterior surface of the shaft for 



I about an inch, giving rise to a triangular impression, the inner half ol 



[which gives insertion to the brachialis anticus. The upper part 



I of this surface, close to the anterior border of the process, affords 



attachment to the anterior ligament of the elbow-joint. The 



{lower pointed portion presents externally a rough prominence, 



I called the tuberosity, \\\nch. gives insertion to fibres of the brachialis 



I anticus, and attachment to the oblique ligament. The anterior 



I margin is sharp, convex, and curved slightly upwards, and it is 



I projected at its outer part into a process, called the beak, which is 



^received into the coronoid fossa of the humerus in flexion of the 



elbow- joint. The inner border gives attachment to the anterior 



(portion of the internal lateral ligament, and at its upper part it 



presents a tubercle for the ulnar head of the flexor sublimis digi- 



torum. Leading downwards from this there is a short ridge for 



origin of the deep head of the pronator radii teres, below which 



