Muscles of the Upper Extremity. 



173 



227. The Muscles at the Shoulder. 



M. dettoides. The clavicular or anterior portion arises from the acro- 

 mial extremity of the clavicle; the acromial or middle portion from the 

 acromion process ; the scapular or posterior portion from the spine of the 

 scapula. It is inserted into the tuberosity on the middle of the outer 

 surface of the humerus. (Raises the arm.) 



Rotators outwards: a) M. supra^p hiatus (Fig. 228) arises 

 from the supraspinous fossa of the scapula and is inserted into the great 

 tuberosity of the humerus. (Raises the arm and rotates it outwards.) 



b) M. infraspinatus (Fig. 228) arises from the infraspinous fossa of 

 the scapula, and is inserted into the great tuberosity of the humerus. 

 (Rotates the arm outwards and draws it downwards.) 



c) M. teres minor (Fig. 228) arises from the upper two thirds of the 

 axillary border of the scapula. It is inserted into the great tuberosity 

 of the humerus. (Rotates the arm outwards and draws it downwards.) 



Rotators inwards: a) M. teres major (Fig. 228) arises from 

 the lower portion of the axillary border of the scapula, and is inserted 

 near the tendon of the M. latissimus dorsi into the posterior bicipital ridge 

 (Spina tuberculi minoris) of the humerus. (Rotates the humerus inwards and 

 draws it downwards and backwards.) 



b) M. subscapularis arises from the subscapular fossa, and is inserted 

 into the lesser tuberosity of the humerus and its neck further down. 

 (Rotates the arm inwards.) 



