THE ELBOW JOINT 79 



by the interosseous and arciform ligaments, and when so united for the 

 purpose of building up the joint may be considered as one bone, since 

 their articular surfaces are in the same curve with which the inferior 

 extremity of the humerus articulates. The joint is of the "hinge" 

 variety, admitting only of flexion and extension, and in contradistinction 

 to the shoulder is well supplied with ligaments, since it possesses two very 

 strong lateral ligaments and an anterior common. But as we have already 

 mentioned, the joint on its outer side is very badly protected. The most 

 common fractures in the neighbourhood of the joint are those affecting 

 the summit of the olecranon process and the beak of the ulna, the former 

 being due to injury caused by a blow, and the latter visually to over- 

 extension of the elbow joint, thus bringing the beak of the ulna too 

 forcibly into contact with the floor of the olecranon fossa of the humerus. 



Running obliquely downwards and inwards across the front of the 

 joint to its insertion into the bicipital tuberosity of the radius is the 

 tendon of the biceps flexor brachii muscle, whilst reflected under the 

 internal lateral ligament of the elbow is the tendon of the brachialis 

 anticus, which obtains insertion into the radius and ulna. 



A rather large cutaneous nerve appears from beneath the biceps. It 

 is one of the terminal divisions of the musculo-cutaneous portion of the 

 median nerve, and it splits into two divisions, namely, anterior and 

 posterior, which accompany the anterior and internal subcutaneous veins 

 respectively of the forearm. 



Upon removing the limb from the trunk we find that the inner 

 aspect of the joint is well protected by muscle, since it is clothed by the 

 broad muscular sheet, the posterior superficial pectoral, which over the 

 joint is of considerable thickness. 



Several important vessels and nerves cross the joint on the inner side 

 of the limb. The posterior radial artery begins above the inner condyle 

 of the humerus, where it may be said to be the direct continuation of the 

 brachial artery, since it is so much larger than the other terminal division 

 of the latter, namely, the anterior radial. It lies first on the humerus, 



