THE SCAPULO-CLAVICULAR ARCH. 



165 



The acromio-clavicular articulation is a synovial joint uniting the outer 

 extremity of the clavicle with the inner edge of the acromion. Both articular sur- 

 faces are covered with fibro-cartilage. The articulation is supported above by a 

 thick and broad superior ligament, and below by an inferior ligament which is very 

 thin. A small interarticular filro-cartilage is sometimes present. It is wedge-shaped, 

 attached by its base to the superior ligament, and projects only a short distance 

 between the articular surfaces. In rare cases it effects a complete division of the 

 joint. 



The coraco-clavicular ligament, which connects the clavicle with the coracoid 

 process of the scapula, is divisible into two parts. The conoid ligament, which is the 

 posterior and internal fasciculus, broad above, narrow below, is attached inferiorly to 

 the inner part of the root of the coracoid process, and superiorly to the conoid 



Fig. 192. VIEW PROM BEFORE OP THE ARTICULATIONS OP THE SHOULDER- BONES. (Allen Thomson.) J 



1, acromio-clavicular articulation ; 2, conoid, and 3, trapezoid part of the coraco-clavicular liga- 

 ment ; 4, near the suprascapular ligament ; 5, on the coracoid process, points to the coraco-acromial 

 ligament ; 6, capsular ligament of the shoulder- joint ; 7, coraco-humeral ligament ; above 6, an 

 aperture in the capsular ligament through which the synovial membrane is prolonged under the tendon 

 of the subscapularis muscle ; 8, tendon of the long head of the biceps muscle ; 9, right half of the 

 interclavicular ligament; 10, interarticular fibro-cartilage of the sterno-clavicular articulation; 11, 

 costo-clavicular ligament ; 12 and 13, cartilage and small part of the second and third ribs attached by 

 their anterior chondro-sternal ligaments. 



tubercle of the clavicle : its fibres are directed backwards and upwards. The trapezoid 

 ligament, the anterior or external fasciculus, slopes upwards, backwards and outwards 

 from the posterior half of the upper surface of the coracoid process to the trapezoid 

 line, on which it is inserted into the clavicle. In the angle between the conoid and 

 trapezoid ligaments there is frequently a synovial bursa. 



A complete synovial joint is occasionally formed between the clavicle and the first rib- 

 cartilage internally, or between the clavicle and the coracoid process externally. 



Movements, &c. The clavicle is firmly bound down at its inner end in the sterno- 

 clavicular articulation, and upon this as a centre it can be moved upwards and downwards, 

 forwards and backwards, or in any intermediate direction, necessarily carrying with it the 

 scapula, which glides in a corresponding direction over the thoracic wall. The scapula farther 

 undergoes a movement of rotation, by which the acromion is raised and the glenoid cavity 



M 2 



