THE FOREARM. 8 1 



longus and the brachialis anticus muscles. After supplying the supinator longus and the extensor 

 carpi radialis longior and brevior muscles, the nerve divides above the external condyle into the 

 radial (a sensory branch) and the posterior interosseous (a motor branch for the extensor muscles 

 of the forearm). 



The elbow- joint is composed of three articulations: 



1. The trochlear surface of the humerus with the greater sigmoid cavity of the ulna. 



2. The capitellum of the humerus with the cup-shaped depression on the head of the radius. 



3. The lesser sigmoid cavity of the ulna with the circumference of the head of the radius. 

 The first articulation is for flexion and extension, the third is for rotation (pronation and supi- 



nation), and the second permits not only of flexion and extension, but also of rotation. All three 

 articulations are surrounded by a common lax capsular ligament, which is attached anteriorly 

 above the coronoid and radial depressions, excluding the epicondyles, and posteriorly above 

 the olecranon fossa, which is also situated within the joint. To either side of the olecranon the 

 capsular ligament forms small diverticula which are situated beneath the cutaneous depressions 

 visible in this situation in the living subject (see page 79). The capsular ligament is attached to 

 the edges of the greater and lesser sigmoid cavities of the ulna in such a way that the apex of the 

 coronoid process and the olecranon are within the articular cavity; this ligament is also inserted 

 into the neck of the radius so that the head of this bone is entirely within the joint. 

 The capsular ligament is reinforced by three other ligaments: 



1. The internal lateral ligament, which radiates from the internal epicondyle to the edge of 

 the greater sigmoid cavity of the ulna. 



2. The external lateral ligament, which runs downward from the external epicondyle, some of 

 the fibers surrounding the neck of the radius and being inserted into the anterior and posterior 

 margins of the lesser sigmoid cavity of the ulna. 



3. The orbicular ligament, which enforces the capsule in a circular manner about the neck 

 of the radius and is inserted into the anterior and posterior margins of the lesser sigmoid 

 cavity of the ulna. The external lateral and orbicular ligaments form practically one continuous 

 band of connective tissue. 



As the large superficial and deep vessels of this region are situated in front of the elbow-joint, 

 it follows that marked subcutaneous or deep extravasations of blood may result from a backward 

 dislocation of both bones, and particularly from that form which is due to hyperextension. In 

 this dislocation the median nerve is necessarily lacerated, as it is also in front of the articulation. 

 The importance of the relation of the ulnar nerve to the joint has been already emphasized (see 

 page 80). 



THE FOREARM. 



The musculature of the forearm surrounds the radius and ulna and their connecting interos- 

 seous membrane in such a way that both bones may be felt through the skin, the ulna throughout 

 its entire extent and the radius in the lower two-thirds of the forearm. Upon the flexor surface 

 in the median line above the wrist may be seen more or less distinctly the tendon of the palman 

 longus muscle (although it is sometimes absent), to the outer side of which the tendon of the 



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