ANATOMY IN A NUTSHELL. 75 



Articulation. — It articulates with four bones, the humerus, ulna, scap- 

 hoid and semilunar. 



Muscles. — It has nine muscles attached, the Biceps, third head of the 

 Flexor sublimis digitorum. Supinator brevis, Flexor longus pollicis, Pronator 

 quadratus, Pronator radii teres. Supinator longus, Extensor ossis metacarpi 

 pollicis and Extensor brevis pollicis. 



Blood Supply. — The nutrient artery is derived from the anterior inter- 

 osseous trunk: it enters the shaft near the middle of the anterior surface, and 

 runs towards the proximal end of the bone. The head of the hone is supplied 

 by the radial recurrent and interosseous recurrent arteries. The lower end is 

 supplied by the anterior and posterior interosseous arteries and numerous 

 twigs from carpal arches. 



LESSON XVII 



The Ulna (Plates XXIY-XXY.) is the longer of the two bones of the fore- 

 arm; its proximal extremity islarger than that of the radius, while its distal ex- 

 tremity is smaller than that of the radius. On cross section it is triangular, but its 

 distal part is more circular. It has a proximal and distal extremity and a dia- 

 physis. The proximal extremity has the olecranon process and the greater 

 and lesser sigmoid cavities. The olecranon (meaning head of elbow) is con- 

 cave from above down, and convex transversely on its articular surface 1 which 

 is covered with cartilage in the recent state. Its margins give attachment to 

 the capsular ligament of the elbow. This surface makes the greater part of 

 the greater sigmoid cavity. On its inner surface is a tubercle for the ulnar 

 origin of the Flexor carpi ulnaris. The internal lateral ligament has an attach- 

 ment in front of the tubercle. The other surface gives attachment to part of 

 the Anconeus. 



The extremity of the process fits into the olecranon fossa of the ulna when 

 the arm is extended. Its upper surface has a concave impression for the ten- 

 don of the Triceps and the anterior margin for the posterior ligament. The 

 posterior surface is covered by a bursa. The coronoid (like a crown) makes 

 the lower part of the greater sigmoid cavity and the upper pari of the bone. 



Its upper surface is covered with cartilage in the recent state. When the 

 arm is flexed it fits in the coronoid impression of the humerus. <>n its outer 

 surface is the lesser sigmoid cavity for the head of the radius. The orbicular 

 ligament is attached to the margin of the lesser sigmoid cavity. 



On it> inferior surface is an impression for the insertion of the Brachialis 

 anticus. Where it joins the shaft of the ulna is the tubercle for the attach- 

 ment of the oblique ligament. On the inner surface is the attachment of the 

 internal ligament, one attachment for tin- Flexor sublimis digitorum; Behind 

 this is a depression for the attachment of the flexor profundus digitorum, anddis- 

 lally from this one for the Pronator radii teres, and occasionally one attach- 

 ment for the Flexor longus pollicis. 



The greater and lesser sigmoid cavities have been described with these two 

 processes. The diaphysis has three borders and three surfaces. The anterior 

 border extends from the inner angle of the coronoid process to the from of the 

 styloid process; for most of the extent it is smooth and rounded. It separates 

 the anterior and internal surfaces andgives attachment to the Flexor profundus 



