156 



THE SKELETON 



partly to the olecranon, the thick upward projection from the shaft, and partly 

 to the coronoid process, which projects horizontally forward from the front of the 

 ulna. This semilunar excavation forms the semilunar notch (greater sigmoid 

 cavity) and articulates wdth the trochlear surface of the humerus. The olecranon 

 is the large curved eminence forming the highest part of the bone. 



The superior surface of the olecranon, uneven and somewhat quadrilateral in shape, receives 

 behind, where there is a rough impression, the insertion of the triceps, and along the anterior 

 margin the articular capsule of the elbow-joint. The posterior surface, smooth and triangular 

 in outline, is separated from the skin by a bursa. The anterior surface, covered with cartilage 

 in the recent state, is du-ected downward and forward, and its margins give attachment to the 

 articular capsule of the elbow-joint. This sm'face, as already noticed, forms the upper and back 

 part of the semilunar notch. On the medial surface of the olecranon is a tubercle for the origin 

 of the ulnar head of the flexor carpi ulnaris, and in front of this a fasciculus of the ulnar collateral 

 ligament of the elbow-joint is attached to the bone; the lateral surface is rough, concave, and 

 gives insertion to a part of the anconeus. The extremity of the olecranon lies during extension 

 of the elbow in the olecranon fossa of the humerus. 



Fig. 185. — Ossification of the Radius and Ulna; the Figure also shows the Relations 

 OF the Epiphysial and Capsular Lines. 



Appears at the tenth 3'ear; fuses c.t the 

 sixteenth year 



Capsular line 



Capsular line 



Radius 



Appears at the second year; fuses at 

 the twentieth year 



Appears at the fifth year; fuses at tho 

 seventeenth year 



Ulna 



Appears at the fourth year; fuses at 

 eighteenth year 



Capsular line 



'I'hc coronoid process, forming the lower and anterior part of the semilunar 

 notch, has a superior articular surface continuous with the anterior surface of the 

 olecranon, and, like it, covered with cartilage. The inferior aspect is rough and 

 concave, and gives insertion to the brachialis. 



It is continuous with tho volar surface; of tlic shaft, and near the junction of the two is a 

 rough oniinonce, named the tuberosity of the ulna, wliich receives the attachment of the oblique 

 Corel of the radius and the insertion of tho brachialis. The medial side presents above a smooth 

 tubercle for the origin of tho ulnar jjortion of the flcror diqilorum subiimis, and a ridge below 

 for tho lessor head of tho pronator teres atid tlio rounded accessory bundle of the flexor pollicis 

 longiis, whilst inirnodiatoly behind the subiimis tubercle there is a triangular depressed surface 

 for the upper fibres of the ^exor digitorum profundus. 



