38 



ULNA. 



Fig. 22. 



foramen, and above it is a shallow spiral groove for the musculo- 

 spiral nerve and profunda major artery. 



The inferior extremity is flat and broad ; anteriorly it is covered 

 by the brachialis anticus muscle, and posteriorly by the triceps. 

 Externally, there is a ridge*^ leading to the external condyle,'^^ from 

 which arise the supinator and extensor muscles. Internally a ridge'^ 

 leads to the iyiternal condyle^'^ which is more prominent than the 

 external, and from which arise the flexor muscles of the forearm. 



The articular surface for the elbow consists of a hemispherical 

 head" for the radius, and an irregular cylinder*^ for the ulna. Above 

 this articular surface, and in front, is a fossa,*'' called the lesser sig- 

 moid cavity, which receives the coronoid process of the ulna in 

 extreme flexion ; behind is a larger fossa, the greater sigmoid, for 

 the olecranon in extreme extension. 



ULNA. 



The forearm consists of two bones — Radius and Ulna. The 

 ulna is the longer and is placed on the inner side, reaching from the 

 elbow to the wrist. 



The upper extremity is the larger, and has a hook-like process 

 behind"* called olecra^ion, to which is inserted the 

 triceps extensor cubiti. In front, is the coronoid 

 'process,^ the base of which has a roughness for the 

 insertion of the brachialis anticus muscle. Be- 

 tween the olecranon and coronoid processes, is the 

 greater sigmoid cavity,^ for articulation with the 

 humerus; continuous with this is the lesser sig- 

 moid cavity,^ upon the outside of the coronoid pro- 

 cess, for the articulation of the head of the radius. 

 Behind the lesser sigmoid cavity, is a triangular, 

 uneven surface, for the insertion of the anconeus 

 muscle. This surface is limited by a ridge 

 giving origin to the supinator radii brevis muscle. 

 The body is prismatic ; the anterior surface* is 

 occupied in its upper three-fourths by the flexor 

 profundus, and in the lowest fourth, by the pro- 

 nator quadratus muscle. The posterior surface is 

 occupied by the extensors of the thumb and the 

 indicator muscle. 



The external edge'' is the sharpest, for the at- 

 tachment of the interosseous ligament. 



The lower extremity, has a small rounded head,^ 

 the outer side of which has a smooth articular sur- 

 face for the radius. From the inner side, there 

 projects^ the styloid process, to which is attached 

 the internal lateral ligament ; behind this process is a groove, in 

 which glides the tendon of the extensor carpi ulnaris muscle. 



