ARTICULATIONS OF THE UPPER EXTREMITIES. 285 



2. Of the Scapulo-Clavicular Articulations. 



These exist at three places; the first by a junction between 

 the acromion scapulae and the external end of the clavicle; and 

 the last two by ligaments sent from the coracoid process to the 

 under surface of the clavicle. 



The Acromio-Clavicular Articulation presents, on each bone, 

 a small oblong face, covered with cartilage. The fibrous cap- 

 sule which invests it is very strong and thick, so as to give the 

 appearance of a much greater extent to the articular faces of 

 the bones than really exists. This capsule is strengthened by 

 additional fibres on its upper surface, passing from one bone to 

 the other, and sometimes called the superior ligament: they are 

 parallel to each other, and somewhat blended with the tendi- 

 nous fibres of the deltoid and trapezius muscles. The capsule 

 is also strengthened on its lower face, by additional fibres, con- 

 stituting the inferior ligament; they are not so abundant as the 

 superior, and pass from the margin of one bone to that of the 

 other, after the same manner. A synovial membrane is reflect- 

 ed over these articular surfaces, and contains but a very small 

 quantity of fluid. In some instances, an inter-articular fibro- 

 cartilage is found in this joint; as in the sterno-clavicular; in 

 such case there is a double synovial membrane. 



Of the Coraco-Clavicular Ligament. -This ligament is double, 

 one part being called the Conoid (Lig. Conoides,) and the other, 

 the Trapezoid (Lig. Trapezoides.) It arises from the roughness 

 at the root of the coracoid process, and is attached to the under 

 surface of the clavicle. The conoidal portion, having its base 

 upwards, is inserted into the tubercle, near the external end of 

 the clavicle. Its fibres are compact, strong, and diverging. The 

 trapezoid is placed at the acromial side of the other. It is qua- 

 drilateral, longer, broader and thinner than the other, having its 

 fibres separated by small interstices; and arising also from the 

 root of the coracoid process, it is inserted into an oblique line 

 leading from the tubercle of the clavicle to its acromial end. 

 The union of these two portions behind forms a projecting angle; 

 in front there is a depression between them filled with fat and 



