THE ELBOW JOINT 



181 



which arise on the scapular tuberosity and end on the Hps of the bicipital groove. 

 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 seldom or never occurs. The large 

 extent 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 hgaments are: ex- 

 ternally, the supraspinatus, infraspinatus, and teres minor; internally, the subscapularis; in 

 front, the biceps and supraspinatus; behind, the triceps. 



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, l)ut does not exceed 

 33°, when all the muscles are removed 

 (Franck). 



THE ELBO^C^ JOINT 



This, the cubital articulation (Articu- 

 latio cubiti), is a ginglymus formed be- 

 tween the distal extremity of the humerus 

 and the proximal ends of the bones of the 

 forearm. 



The articular surfaces are: (1) A 

 trochlear surface formed by the condyles 

 of the humerus and the groove between 

 them ; (2) the corresponding glenoid cavi- 

 ties and ridge on the proximal extremity 

 of the radius, together with the semilunar 

 notch of the ulna. 



Olecranon 



foasa 



External lateral 

 ligament 



Transverse or 

 arciform 

 ligament 



Fig. 



143. — Left Elbow Joint of Horse, Poste- 

 rior View. The Capsule is Removed. 

 (After Schmaltz, Atlas d. Anat. d. Pferdes.) 



The articular surface of the condyles does 

 not extend 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 outer condyle is smaller 



than that of the inner one, and is subdivided 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 

 fossae. 



The joint capsule is extremely thin behind, where it forms a pouch in the ole- 

 cranon fossa under the anconeus muscle and a pad of fat. In front it is strength- 

 ened by oblique fibers (Ligamentum obliquum or anterior ligament) , and laterally 

 it fuses with the lateral ligaments. Small pouches of the synovial membrane 

 lubricate the origins of the flexors of the carpus and digit and the small radio-ulnar 

 joints. There are two lateral ligaments. 



The internal lateral ligament (Ligamentum collaterale radiale) is attached 

 above to an eminence on the internal epicondyle of the humerus, and divides into 

 two parts: the long, superficial part ends on the inner border of the radius, just 

 below the level of the interosseous space; the deep, short part is inserted into the 

 internal tuberosity of the radius. (The superficial part represents the pronator teres 

 muscle, which is only exceptionally present in the horse.) 



