170 THE ARTICULATIONS OF THE UPPER LIMB. 



inwards, from the interosseous border of the radius to that of the ulna. Its superior 

 border is placed about an inch below the tuberosity of the radius, leaving an open 

 space above (hiatus interosseus) through which the posterior interosseous vessels pass. 

 This space is bounded above by the oblique ligament, a flattened bundle of fibres 



Fig. 197. THE LOWER PARTS OF THE RADIUS AND TILNA, WITH THE 



TRIANGULAR FIBRO-CARTILAGE CONNECTING THEM. (11. Quain. ) 



1, ulna ; 2, its styloid process ; 3, radius ; 4, articular surface for 

 the scaphoid bone ; 5, that for the lunar bone ; 6, lower surface of 

 the triangular fibro-cartilage ; * *, a piece of whalebone passed be- 

 tween the fibro-cartilage and the ulna. 



directed downwards from the outer part of the tuberosity 

 of the ulna, to be attached to the radius close below the 

 tuberosity : it varies much in size, and is frequently 

 wanting. Other small bundles of fibres, having the 

 same direction as the oblique ligament, are often to be 



found at intervals, decussating with the fibres of the interosseous ligament on 



its posterior surface. 



Movement of the radius on the ulna. The disposition of the annular ligament allows 

 the head of the radius to rotate freely within it. while the lower end of the radius, being 

 bound by the triangular fibro-cartilage to the styloid process of the ulna, undergoes, in 

 addition to the rotation, a movement of circumduction round that point, by which the hand 

 is brought intp the prone or the supine position. Thus in pronation and supination the 

 radius describes a part of a cone, the axis of which extends from the centre of the head of 

 the radius to the styloid process of the ulna. The range of movement between the radius and 

 ulna is rather less than 180. Accompanying the movement of the radius in the pronation 

 and supination of the hand, there is generally a less extensive movement of circumduction on 

 the part of the ulna in a direction opposite to that in which the lower end of the radius- 

 travels. The circumduction of the ulna is produced by a slight degree of flexion or extension, 

 together with a corresponding lateral movement, having their seat in the articulation of the 

 elbow, and is not accompanied by any appreciable rotation of this bone. (J. Heiberg, k - Ueber 

 die Drehungen der Hand," 1884, and Journ, Anat., xix ; T. Dwight, Journ. Anat., xix ; C. W. 

 Cathcart, Journ. Anat., xix.) 



THE ELBOW-JOINT. 



The lower extremity of the humerus is in contact with the ulna and radius at 

 the elbow, and forms with them a hinge-joint. The great sigmoid cavity of the 

 ulna articulates with the trochlea of the humerus, so as to admit of flexion and 

 extension ; while the cup-shaped depression on the head of the radius can in addition 

 turn freely on the rounded capitellum. In the sigmoid cavity the articular 

 cartilage is usually wanting over a narrow area which extends across a central 

 constriction produced by a marginal notch on each side between the olecranon and 

 the coronoid process. The fibrous capsule surrounding the joint is thickened on the 

 two sides, forming strong lateral ligaments, and the thinner portions in front and 

 behind are known as the anterior and posterior ligaments. The orbicular ligament 

 of the superior radio-ulnar articulation, which has already been described, is also a 

 part of this capsule. 



The internal lateral ligament, triangular in shape, consists of anterior and 

 posterior thickened bands, and an intermediate thinner part. The anterior band 

 springs from the lower and fore part of the internal condyle of the humerus, and is 

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

 The posterior part, broader and stronger, passes from the under and back part of 

 the condyle to the inner border of the olecranon ; and the intermediate fibres are 



