364 A MANUAL OF ANATOMY. 



Nerve Supply. The circumflex, which furnishes fibres 

 from the fifth and sixth cervical nerves. 



Action. To abduct the arm to a right angle with the 

 body. The anterior portion of the muscle will flex and ad- 

 duct the arm to (less than) a right angle, while the poste- 

 rior portion will adduct and extend the arm to half a right 

 angle. 



The elevation of the arm beyond a right angle is ac- 

 complished through the action of the trapezius and serratus 

 magnus muscles by producing a rotation of the scapula 

 and elevation of the outer end. The clavicle moves up- 

 ward and at the same time rotates upon its long axis. 



The deltoid really is a continuation of the direction of 

 the fibres of the trapezius and so extends its action. 



DISSECTION. 



Cut the trapezius away from its insertion, divide the nerves passing to it, 

 and roll the muscle up to the spine. 



Complete the cleaning of the latissimus dorsi muscle. 



The Latissimus Dorsi. 



Origin. From the spines and supraspinous ligaments of 

 the lower six dorsal and all the lumbar vertebrae, and 

 through the lumbar aponeurosis, from the spines of the 

 sacral vertebrae and the outer lip of the posterior third of 

 the crest of the ilium, from the outer surface of the three 

 or four lower ribs external to their angles, and from the 

 outer surface of the lower angle of the scapula. 



Insertion. Into the bottom of the bicipital groove of 

 the humerus. 



Nerve Supply. The long or second subscapular nerve. . 

 The filaments coming from the fifth cervical nerve. 



Action. The origin being the fixed point, the muscle acts 

 to draw the humerus (and shoulder) downward, backward, 



