THE ELBOW JOINT 



219 



(2) on the humerus, the head. Both surfaces are approximately spherical and 

 similar in curvature, but the hvuneral surface is about twice as extensive as that of 

 the scapula. 



The joint capsule is ample enough to allow the bones to be drawn apart about 

 an inch (ca. 2-3 cm.) ; but this requires a very considerable amount of force unless 

 air is admitted into the joint cavity. The fibrous layer is not attached to the mar- 

 gin of the joint surfaces, but at a distance of one to two centimeters from it. It is 

 strengthened in front by two diverging elastic bands, which arise on the tuber 

 scapulje and end on the tuberosities of the humerus. A pad of fat is interposed 

 between the capsule and the tendon of the biceps. 



Ligaments are absent from this joint, but the muscles and tendons around it 

 afford remarkable security, so that dislocation very seldom occurs. The large ex- 

 tent of the head of the humerus is also of importance in this regard. 



The principal muscles which are attached around the joint and act as ligaments are: 

 laterally, the supraspinatus, infraspinatus, and teres minor; medially, the subscapularis ; in 

 front, the biceps and supraspinatus; behind, the triceps. Fibers of the brachiaUs are attached to 

 the lower edge of the posterior part of the joint capsule, and would e"\ndently tense the latter. In 

 some cases the joint cavity communicates with the bicipital or intertuberal bm-sa. 



Movements. — While it is a typical enarthrosis in structure, and capable of the 

 various movements of the ball-and-socket joint, the chief normal movements are 

 flexion and extension. In the position of rest the angle formed between the scapula 

 and humerus posteriorly is about 110° to 120°; in flexion it is reduced to about 80°, 

 and in extension it is increased to about 145°. Adduction and abduction are very 

 restricted, the former being limited chiefly by the infraspinatus, the latter by the 

 subscapularis and the low insertion of the superficial pectoral muscles. Rotation 

 is somewhat freer, but does not exceed 33° when 

 all the muscles are removed (Franck). 



Oleciarion 

 Jossa 



THE ELBOW JOINT 



This, the cubital articulation (Articulatio 

 cubiti), is a ginglymus formed between the dis- 

 tal extremity of the humerus and the proximal 

 ends of the radius and ulna. 



The articular surfaces are: (1) A trochlear 

 surface formed by the condyles of the humerus 

 and the ridge between them; (2) the correspond- 

 ing glenoid cavities and groove on the proxunal 

 extremity of the radius, together with the semi- 

 lunar notch of the ulna. 



The articular surface of the condyles does not ex- 

 tend upon the back of the extremity, but the groove which 

 receives the semilunar notch of the ulna extends up into 

 the olecranon fossa. In the fore part of the groove there 

 is a synovial fossa. The surface on the lateral condyle is 

 much smaller than that of the medial one, and is sub- 

 divided into two unequal parts by a shallow furrow. On 

 the lower part of the semilunar notch and the adjacent 

 part of the ridge on the radius are synovial fossEe. 



The joint capsule is extremely thin behind, 

 where it forms a pouch in the olecranon fossa 



under the anconeus muscle and a pad of fat. In front it is strengthened by 

 oblique fibers (lig. obliquum or anterior ligament), and on each side it fuses 

 with the collateral ligaments. It also is adherent to the tendons of muscles 

 which arise from the distal end of the humerus or end on the proximal end of the 

 radius. The synovial membrane sends prolongations to the small radio-ulnar 



Lateral 

 ligament 



Transverse or 

 arciform 

 ligament 



Fig. 234. — Left Elbow Joint of Horse; 

 Posterior View. The Capsule is Re- 

 moved. (After Schmaltz, Atlas d. Anat. 

 d. Pferdes.) 



