THE ELBOW-JOINT. 



The internal lateral ligament, composed of diverging and radiating fibres, 

 is divisible into an anterior and a posterior part. The anterior part radiates 

 from the front of the internal condyloid eminence of the humerus, and is 

 inserted into the coronoid process, along the inner margin of the sigmoid 

 cavity. The posterior part, of the same triangular form, passes from the 

 under and back part of the condyloid eminence downwards to the inner 

 border of the olecranon ; and some fibres are connected with a small transverse 

 band over the notch between the olecrauon and the coronoid process. 



The external lateral ligament, intimately connected with the tendinous 

 attachment of the extensor muscles, is shorter and much narrower than the 

 internal. It is attached superiorly to the external condyloid eminence of 

 the humerus, and inferiorly becomes blended with the annular ligament 

 of the radius ; some of its hinder fibres are prolonged to the external margin 

 of the ulna. 



The anterior ligament consists of a thin sheet of fibres extending down- 

 wards from above the coronoid pit of the humerus, and protecting the 

 anterior part of the synovial membrane ; it is strongest in its middle part. 



The posterior ligament is comparatively thin 



and weak, and consists of loose and irregular fibres Fig. 131. 



passing transversely across the olecranon fossa of the 

 humerus, and from the sides of that fossa to the 

 olecranon process, thus completing the capsule of 

 the joint behind. 



Fig. 131. VERTICAL ANTERO-POSTERIOR SECTION OP THE 

 ELBOW-JOINT THROUGH THE GREATER SIGMOID CAVITY 

 OF THE ULNA AND CORRESPONDING TROCHLKAR SURFACE 

 OF THE HUMERUS. J 



1, cut surface of the humerus ; 2, that of the ulna ; 3, 

 posterior part, and 4, anterior part of the synovial cavity of 

 the joint ; 5, orbicular ligament enclosing the head of the 

 radius ; 6, tendon of the biceps muscle at its insertion into 

 the tuberosity ; 7, is at the lower end of the round ligament. 



The synovial membrane extends upwards on the 

 humerus so far as to line the fossse for the coronoid 

 and olecranon processes, and is loose and vascular in 

 the latter positions. It is prolonged round the head 

 and neck of the radius, which it separates from the 

 smaller sigmoid cavity and annular ligament. 



MOVEMENTS. Flexion and extension are the only movements which can take place 

 between the humerus and ulna ; aud these are limited by the locking of the coro- 

 noid and olecranon processes in the respective fossae of the humerus which receive 

 them. The path of motion is in a nearly vertical plane, with a direction slightly 

 outwards. The inner lip of the trochlea being prominent below, forms an expansion 

 which corresponds to an inward projection of the coronoid part of the ulnar surface, 

 and is only brought into use in flexion ; and the outer lip of the trochlea, being everted 

 at the upper and back part, forms a surface which is only in use in complete extension, 

 and which then corresponds to a surface on the outer aspect of the olecranon, which 

 comes into contact with no other part of the humerus. In flexion and extension the 

 radius moves by its cup-shaped head upon the capitulum, and on the groove between 

 that process and the trochlea, by a ridge internal to the cup. It is most completely 

 in contact with the humerus in the position of semi-flexion and semi-pronation. In 

 full extension and supination, the anterior margin of the head of the radius is barely 

 in contact with the inferior surface of the capitulum. In full flexion, the margin of 

 the head of the radius rests against the pit above the capitulum. 



