THE ELBOW-JOINT. 



351 



ulna. This ligament is intimately blended with the tendon of origin of the 

 Supinator brevis muscle. 



The Synovial Membrane is very extensive. It covers the margin of the 

 articular surface of the humerus. and lines the coronoid and olecranon fossae on 

 that bone ; from these points it is reflected over the anterior, posterior, and 

 lateral ligaments, and forms a pouch between the lesser sigmoid cavity, the 

 internal surface of the orbicular ligament, and the circumference of the head of 

 the radius. 



Between the capsular ligament and the synovial membrane are three masses 

 of fat ; one. the largest, above the olecranon fossa, which is pressed into the fossa by 

 the triceps during flexion ; a second, over the coronoid fossa ; and a third, over 

 the radial fossa. These are pressed into their respective fossae during extension. 



The JIuseles in relation with the joint are, in front, the Brachialis anticus; 

 behind, the Triceps and Anconeus; externally, the Supinator brevis and the 

 common tendon of origin of the Extensor muscles ; internally, the common 

 tendon of origin of the Flexor muscles, and the Flexor carpi ulnaris, with the 

 ulnar nerve. 



The Arteries supplying the joint are derived from the communicating branches 

 between the superior profunda, inferior profunda, and anastomotica magna arteries, 

 branches of the brachial, with the anterior, posterior, and interosseous recurrent 

 branches of the ulnar and the recurrent branch of the radial. These vessels form 

 a complete chain of inosculation around the joint. 



The Serves are derived from the ulnar as it passes between the internal con- 

 dyle and the olecranon ; a filament from the musculo-cutaneous (Rudinger), and 

 two from the median (Macalister). 



Actions. The elbow-joint comprises three different portions viz, the joint 

 between the ulna and humerus, that between 

 the head of the radius and the humerus. and 

 the superior radio-ulnar articulation, described 

 below. All these articular surfaces are in- 

 vested by a common synovial membrane, and 

 the movements of the whole joint should be 

 studied together. The combination of the 

 movements of flexion and extension of the 

 forearm with those of pronation and supina- 

 tion of the hand, which is ensured by the two 

 being performed at the same joint, is essen- 

 tial to the accuracy of the various minute 

 movements of the hand. 



The portion of the joint between the ulna 

 and humerus is a simple hinge-joint, and 

 allows of movements of flexion and extension 

 only. Owing to the obliquity of the trochlear 

 surface of the humerus. this movement does 

 not take place in a straight line ; so that 

 when the forearm is extended and supinated 

 the axis of the arm and forearm is not in 

 the same line, but the one portion of the limb 

 forms an angle with the others, and the hand, 

 with the forearm, is directed outward. Dur- 

 ing flexion, on the other hand, the forearm 

 and the hand tend to approach the middle 

 line of the body, and thus enable the hand to 

 be easily carried to the face. The shape of 



the articular surface of the humerus, with its prominences and depressions 

 accurately adapted to the opposing surfaces of the olecranon, prevents any lateral 

 movement. Flexion is produced by the action of the Biceps and Brachialis 



FIG. 247. Sagittal section of the right 

 elbow-joint, taken somewhat obliquely 

 and seen from the radial aspect. (After 

 Braune.) 



