252 



THE ARTICULATIONS 



Movements. — In the movements of the shoulder girdle, the scapula moves upon the lateral 

 end of the clavicle, and the clavicle, in turn, carried by the uniting Ligaments, moves upon the 

 sternum; so that the entire scapula moves in the arc of a circle whose centre is at the sterno- 

 clavicular joint, and whose radius is the clavicle. The scapula, in moving upon the clavicle, 

 also moves upon the thorax forward and backward, upward and downward, and also in a rota- 

 tory direction upon an axis drawn at right angles to the centre of the bone. Throughout these 

 movements the inferior angle and base of the scapula are kept in contact with the ribs by the 



Fig. 286. — Anterior View of Shoulder, showing also Coraco-clavicular and 

 coraco-acromial ligaments. 



Conoid ligament 



Superior transverse scapular ligament ^^ 



"" V Trapezoid ligament 



Coraco-acromial ligament 



Short head of biceps 

 Subscapular tendon 



Capsule of shoulder 



""Long tendon of biceps 



latissimus dor si, which straps down the former, and the rhomboids and serratus anterior (magnus), 

 which brace down the latter. The glenoid cavity could not have preserved its obliquely 

 forward direction had there been no acromio-clavicular joint, but would have shifted round a 

 vertical axis, and thus the shoulder would have pointed medialward when the scapula was 

 advanced, and lateralward when it was drawn backward. By means of the acromio-clavicular 

 joint, the scapula can be forcibly advanced upon the thorax, the glenoid cavity all the time 

 keeping its face duly forward. Thus the muscles of the shoulder and forearm can be with 

 advantage combined, as, for example, in giving a direct blow. The acromio-clavicular joint 

 also permits the lower angle of the scapula to be retained in contact with the chest wall during 

 the rising and falling of the shoulder, the scapula turning in a hinge-like manner round the 

 horizontal axis of the joint. 



There are no actions in which the scapula moves on a fixed clavicle, or the clavicle on a 

 fixed scapula; the two bones, bound together by their connecting ligament, must move in 

 uni.son. 



(c) The Proper Scapular Ligaments 



There arc three proper ligaments of the scapula, which pass between different 

 portions of the bone, viz. — 



Coraco-acromial. Superior transverse. 



Inferior transverse. 



The coraco-acromial ligament (figs. 286 and 290) is a flat, triangular band 

 with a broad base, atlacluMl to the lateral border of the coracoid process, and a 

 blunt apex which is fixed to tin; tip of the acromion. It is made up of two broad 

 marginal bands, and a smaller and thinner intervening portion. The anterior 

 band, which arises from the anterior i)ortion of the coracoid process, is the 

 stronger, and some of its marginal fibres can often be traced into the short head 

 of lh(; bi(;(;ps, which can then make tense this edge of the ligament. The pos- 

 terior band, coming from the posterior part of the coracoid process, is also strong. 



