250 



THE ARTICULATIONS 



Relations. — In front of the joint is the sternal head of the stern o-mastoid. Behind it are 

 the sterno-h3'oid and sterno-thyreoid muscles. Still further back, on the right side, are the 

 innominate and internal mammary arteries, and, on the left side, the left common carotid, the 

 left subclavian, and the internal mammary arteries. Above and behind, between the sterno- 

 mastoid and s^erno-hyoid muscles, the anterior j ugular vein passes back and laterally toward the 

 posterior triangle. 



The movements permitted at this joint are various though limited, owing to the capsular 

 ligament being moderately tense in every position of the clavicle. Motion takes place in 

 nearly every direction — viz., upward, downward, forward, backward, and in a circumductory 

 manner. The. upward and downward motions occur between the clavicle and the articular 

 disc; during elevation of the arm the upper edge of the clavicle with its attached articular disc 

 is pressed into the sternal socket, and the lower edge glides away from the disc; during depression 

 of the limb, the lower edge of the clavicle presses on to the disc, while the rest of the articular 

 surface of the clavicle inclines laterally, bringing with it to a slight degree the upper edge of 

 the articular disc. These movements occur on an antero-posterior axis drawn through the 

 outer compartment of the joint. The forward and backward motions take place between the 

 articular disc and sternum, the clavicle with the disc gliding backward upon the sternum when 

 the shoulder is brought forward, and forward when the shoulder is forced backward; these 

 movements occur round an axis drawn nearly vertically through the sternal socket. 



Fig. 285. — Anterior View op Sterno-costo-clavicular Joint, with Section 

 SHOWING Cavities opened on the Right Side. 



Interclavicular ligament 



Articular disc 



Joint between ster- 

 num and second cos- 

 tal cartilage 



Costa-clavicular liga- 

 , . ^'■•ment 



Sterno-clavicular lig- 

 ament 



The articular disc serves materially to bind the bones together, and to prevent the media 

 and upward displacements of the clavicle. It also forms an elastic buffer which tends to break 

 shocks. The capsule, by being moderately tight, tends to limit movements in all directions, 

 while the interclavicular ligament is a safeguard against upward displacement during depression 

 of the arm. The costo-clavicular ligament prevents dislocation upward during elevation of the 

 arm, and resists displacements backward. 



Muscles which move the clavicle at the sterno-clavicular joint.— Elevators. — Trapezius, 

 clavicular part of sterno-mastoid, levator scapuhe, omo-hyoid, rhomboids. 



Depressors. — Subclavius, pectoralis minor, lower fibres of trapezius and serratus anterior 

 (raagnus). Depression is aided by the weight of the upper extremity. 



Protraclors. — Pectoralis major and minor. Serratus anterior (magnus). 



Relractors. — Latissimus dorsi, trapezius. 



2. THE SCAPULO-CLAVICULAR UNION 



The scapula is connected with the clavicle by a synovial joint with its liga- 

 ments at the acromio-clavicular articulation; and also by a set of ligaments pass- 

 ing botw(!f'n the coracoid process and the clavicle. So that we have to consider — 



{a) The acromio-clavicular articulation. 

 {b) The coraco-clavicular ligaments. 



(c) The proper scapular ligaments are also best described in this section- 

 viz., the coraco-acromial and transverse. 



