296 THE ARTICULATIONS, OR JOINTS 



The capsular ligament (capsula articularis] completely surrounds the articula- 

 tion, consisting of fibres of varying degrees of thickness and strength. Those 

 in front and behind are of considerable thickness, and form the anterior and 

 posterior sternoclavicular ligaments; but those above and below, especially in 

 the latter situation, are thin and scanty. 



The anterior sternoclavicular ligament (ligamentum sternodaviculare) (Fig. 

 243) is a part of the capsule. It is a broad band of fibres which covers the anterior 

 surface of the articulation, being attached, above, to the upper and front part 

 of the inner extremity of the clavicle, and, passing obliquely downward and 

 inward, is attached, below, to the upper and front part of the first piece of the 

 sternum. This ligament is covered, in front, by the sternal portion of the Sterno- 

 mastoid and the integument; behind, it is in relation with the articular disk and 

 the two synovial membranes. 



The posterior sternoclavicular ligament, also a part of the capsule, is a band 

 of fibres which covers the posterior surface of the articulation, being attached, 

 above, to the upper and back part of the inner extremity of the clavicle, and, 

 passing obliquely downward and inward, is attached, below, to the upper and 

 back part of the first piece of the sternum. It is in relation, in front, with the 

 articular disk and synovial membranes; behind, with the Sternohyoid and 

 Sternothyroid muscles. 



The interclavicular ligament (ligamentum interdaviculare) (Fig. 243) is a flat- 

 tened band which varies considerably in form and size in different individuals; 

 it passes in a curved direction from the upper part of the inner extremity of one 

 clavicle to the other, and is also attached to the upper margin of the sternum. 

 It is in 1 relation, in front, with the integument; behind, with the Sternothyroid 

 muscles. 



The COStoclavicular or rhomboid ligament (ligamentum costodaviculare) (Fig. 

 243) is short, flat, and strong; it is of a rhomboid form, attached, below, to the 

 upper and inner part of the cartilage of the first rib; it ascends obliquely back- 

 ward and outward, and is attached, above, to the rhomboid depression on the 

 under surface of the clavicle. It is in relation, in front, with the tendon of origin 

 of the Subclavius; behind, with the subclavian vein. 



The articular disk (discus articularis] (Fig. 243) is a flat and nearly circular 

 meniscus, interposed between the articulating surfaces of the sternum and clavicle. 

 It is attached, above, to the upper and posterior border of the articular surface 

 of the clavicle; below, to the cartilage of the first rib, at its junction with the 

 sternum; and by its circumference, to the anterior and posterior sternoclavicular 

 and the interclavicular ligaments. It is thicker at the circumference, especially 

 its upper and back part, than at its centre or below. It divides the joint into 

 two cavities, each of which is furnished with a separate synovial membrane. 



Synovial Membrane. Of the two synovial membranes found in this articulation, one is 

 reflected from the sternal end of the clavicle over the adjacent surface of the articular disk and 

 cartilage of the first rib; the other is placed between the articular surface of the sternum and 

 adjacent surface of the articular disk; the latter is the larger of the two. 



Movements. This articulation is the centre of the movements of the shoulder, and admits 

 of a limited amount of motion in nearly every direction upward, downward, backward, for- 

 ward as well as circumduction. When these movements take place in the joint, the clavicle 

 in its motion carries the scapula with it, this bone gliding on the outer surface of the thorax. This 

 joint therefore forms the centre from which all movements of the supporting arch of the shoulder 

 originate, and is the only point of articulation of this part of the skeleton with the trunk. "The 

 movements attendant on elevation and depression of the shoulder take place between the clavicle 

 and the articular disk, the bone rotating upon the ligament on an axis drawn from before back- 

 ward through its own articular facet. When the shoulder is moved forward and backward, the 

 clavicle, with the articular disk, rolls to and fro on the articular surface of the sternum, revolving, 

 with a gliding movement, around an axis drawn nearly vertically through the sternum. In the 

 circumduction of the shoulder, which is compounded of these two movements, the clavicle revolves 



