248 



THE A R TICULA TIONS. 



II. Acromio- clavicular Articulation (Fig. 169). 



The Acromio-clavicular is an arthrodial joint formed between the outer 

 extremity of the clavicle and the inner margin of the acromion process of the 

 scapula. Its ligaments are the 



Superior Acromio-clavicular. 

 Inferior Acromio-clavicular. 

 Interarticular Fibro -cartilage. 



( Trapezoid 



Coraco-claviculaix and 

 Conoid. 



The Superior Acromio-clavicular Ligament is a quadrilateral band which 

 covers the superior part of the articulation, extending between the upper part of 

 the outer end of the clavicle and the adjoining part of the upper surface of the 

 acromion. It is composed of parallel fibres which interlace with the aponeurosis 

 of the Trapezius and Deltoid muscles ; below, it is in contact with the inter- 

 articular fibre-cartilage (when it exists) and the synovia! membranes. 



The Inferior Acromio-clavicular Ligament, somewhat thinner than the pre- 

 ceding, covers the under part of the articulation, and is attached to the adjoining 

 surfaces of the two bones. It is in relation, above, with the synovial membranes, 

 and in rare cases with the interarticular fibro-cartilage ; below, with the tendon 



FIG. 169. The left shoulder-joint, scapulo-clavicular articulations, and proper ligaments of scapula. 



of the Supraspinatus. These two ligaments are continuous with each other in 

 front and behind, and form a complete capsule round the joint. 



The Interarticular Fibro-cartilage is frequently absent in this articulation. 

 When it exists it generally only partially separates the articular surfaces, and 

 occupies the upper part of the articulation. More rarely it completely separates 

 the joint into two cavities. 



The Synovial Membrane. There is usually only one synovial membrane in 



