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APPLIED ANATOMY. 



If traction is made on the arm, the muscles are the resisting agents. If the arm 

 is in a position of adduction, those going from the humerus to the scapula, as the 

 deltoid, supraspinatus, biceps, and triceps, act. If in abduction, then also those 

 from the humerus to the trunk, like the pectoralis major and latissimus dorsi, are 

 brought into play. The part played by the deltoid and trapezius should be noted. 

 If the arm is down by the side and traction is made on it, the force is transmitted 

 from the humerus in a direct line through the deltoid and the upper fibres of the 

 trapezius to their attachment to the spine and superior curved line of the occiput. 

 If, on the contrary, the traction is made while the arm is raised above the level of the 



Superior acromioclavicular ligament 



Tendon of supra 

 spinatus muscle 



Acromion process 



Clavicle 



Conoid ligament 

 Trapezoid ligament 



Coraco-acromial ligament 

 bracoid process 



Coracohumeral ligament 

 Coracobrachialis muscle 

 Short head of biceps 



Long head of biceps 



Pectoralis major muscle 



FIG. 367. Acromioclavicular and shoulder joints. 



shoulder, the force is transmitted through the axillary fold muscles as well as by the 

 deltoid and continued through the lower fibres of the trapezius. In either case the 

 muscles are the resisting agents and not the ligaments. Abduction to more than a 

 right angle is resisted by the contact of the greater tuberosity with the under surface 

 of the acromion process and coraco-acromial ligament and the under side of the cap- 

 sular ligament is made tense. The raising of the arm to 90 degrees is performed 

 by the supraspinatus and deltoid muscles of the scapula and beyond this by the 

 serratus anterior and other muscles. 



Inward rotation is limited by the infraspinatus and teres minor muscles and by 

 tension of the upper portion of the capsule. Outward rotation is limited by the sub- 

 scapularis and upper portion of the capsule. 



