THE FORE ARM. 191 



its lower part. To the upper fourth of this ridge, is attached 

 the anconeus muscle, which reposes in a hollow between it and 

 the beginning of the first or outer ridge. To the beginning of 

 this latter ridge, is attached the supinator radii brevis muscle. 

 On the posterior surface of the bone, just below the olecranon, 

 is a long sub-cutaneous triangular face on which we. lean. 



The three ridges of the ulna divide it into as many surfaces, 

 which are each modified by the muscles lying upon them. The 

 anterior surface presents, just above the middle of the bone, the 

 canal for the nutritious artery, running obliquely upwards. 



The body of the ulna is compact, the extremities, and more 

 abundantly the upper, are cellular. 



Of the Radius, (Radius.) 



The radius is shorter than the ulna, is placed on its external 

 side, and extends from the os humeri to the wrist. It is smaller 

 at the humeral than at the carpal extremity, and though nearly 

 straight is somewhat convex outwardly. It is to be considered 

 in its extremities and body. 



The superior or humeral extremity presents a cylindrical 

 head, which bears all around it the marks of a cartilaginous in- 

 crustation, broader on the cubital than on the other side. The 

 broader part plays in the lesser sigmoid cavity of the ulna, while 

 the other is in contact with the annular ligament. A superficial 

 fossa also exists on the upper surface of this head, which re- 

 ceives the convexity of the articular face of the external con- 

 dyle of the os humeri. The head of the radius is placed upon 

 a narrow part called the neck, of about half an inch in length. 

 Immediately below the neck, on the ulnar side, is a rough pro- 

 . tuberance or tubercle, the bicipital, for the insertion of the bi- 

 ceps flexor cubiti. 



The lower or carpal extremity of the bone, is augmented con- 

 siderably in volume, and is flattened out transversely. The 

 carpal surface presents a long superficial cavity, bounded ex- 

 ternally by the styloid process, from which proceeds the exter- 

 nal lateral ligament; and ending on its ulnar side, by a small 



