THE SUPERIOR EXTREMITY 



the clavicle, the more mobile bone, is larger than the sternal 

 facet, and, below, it comes into contact with the first costal 

 cartilage. A somewhat loose capsule, lined with synovial 

 membrane, is attached to the margins of the articular surfaces. 

 It is thickened in front and behind by the anterior and posterior 

 sterno-clavicular ligaments. Anteriorly, the sterno-clavicular 

 joint is covered by the sternal head of the sterno-mastoid, and, 

 posteriorly, it is in relation to the sterno-hyoid and the sterno- 

 thyreoid muscles. 



Joint capsule 

 Joint cavity 



Interarticular 

 ligament 



Joint cavity 



Anterior chondro- 

 sternal ligament 



FIG. 4. Sterno-Clavicular and Costo-Sternal Joints. 



The joint is divided into a medial or inferior and a lateral 

 or superior compartment by a disc-shaped meniscus, which is 

 attached to the clavicle above, the first costal cartilage below, 

 and to the capsule in front and behind. When the arm is 

 hanging by the side the upper compartment is V-shaped, but 

 when the arm is raised the upper part of the disc is thrust 

 medially by the clavicle, and both compartments become slit- 

 like. The disc acts as a buffer between the clavicle and the 

 sternum and serves to diminish the results of indirect violence. 



Two accessory ligaments strengthen the joint : (i) The 



