THE LATERAL THORACIC REGION 



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ligaments; inserted into the junction of the first rib with its 

 cartilage between the fibers of the costoclavicular ligament. 

 2. M. pectoralis minor from three ribs near their cartilages, 

 usually the third, fourth, and fifth, often the second, third, 

 and fourth or fifth, and from the intercostal aponeuroses; 

 insertion, inner border and upper surface of the coracoid; 

 a bursa is under its insertion (1 in 40 cases). 



The Lateral Thoracic Region 



M. serratus magnus, placed between the ribs and scapula. 

 Origin, first eight or nine ribs by as many slips; the first slip 

 is attached to two ribs; insertion, posterior border of the scapula 

 and into the flat surfaces or anterior aspects of the upper and 

 lower angles, not in the subscapular fossa. There are three 

 sets of fibers: (1) First digitation from the first and second 

 ribs, passes up to the flat area at the upper angle; (2) second 

 and third digitations, from the second and third ribs, pass 

 down in a thin triangular layer to the whole line between the 

 upper and lower angles; (3) the remaining five or six digita- 

 tions converge, some up and some down, to the flat surface 

 in front of the lower angle. 



Nerves. The pectoralis major by the two anterior thoracics; 

 the minor by the internal anterior thoracic nerve; the sub- 

 clavius by the fifth and sixth cervical; serratus magnus by the 

 posterior thoracic, upper division by the fifth cervical, middle 

 by the sixth cervical (often fifth cervical also), lower by the 

 sixth and seventh cervical. 



Actions . Pectoralis major. 



Arm at side. 



First part of the 

 muscle draws the 

 arm up and in. 



Second part of the 

 muscle draws the 

 arm down and 

 rotates in. 



Arm abducted to 90 

 degrees. 



Draws the arm for- 

 ward and rotates 

 in. 



Draws the arm 

 down, in, and 

 rotates in. 



Arm raised high. 

 Draws the arm for- 

 ward to horizontal, 



and no farther. 

 Adducts, and draws 



down. 



It assists the latissimus dorsi in adduction, opposes it in flexion; 

 the lowest fibers are the best adductors; succeeding ones draw 



