THE ELBOW JOINT 219 
(2) on the humerus, the head. Both surfaces are approximately spherical and 
similar in curvature, but the humeral 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 em.); 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 
scapulze 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 brachialis are attached to 
the lower edge of the posterior part of the joint capsule, and would evidently tense the latter. In 
some cases the Joint cavity communicates with the bicipital or intertuberal bursa. 
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). 
THE ELBOW JOINT Olecranon 
This, the cubital articulation (Articulatio HOSE 
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 Peer 
and the ridge between them; (2) the correspond- ligament | 
ing glenoid cavities and groove on the proximal 
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 foss 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 fosse. 
Transverse or 
arciform 
ligament 
Fic. 234.—Lerr Exvsow Joint or Horss; 
Posterior View. THE Capsue 1s RE- 
MOveED. (After Schmaltz, Atlas d. Anat. 
The joint capsule is extremely thin behind, d. Pferdes.) 
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 
