pectoralis major

pectoralis major (plural pectoralis majors or pectorales majores)

1. (anatomy) The large muscle that covers the chest and ribs.

   Synonym: (informal) pec

   • 2010, Siddhartha Mukherjee, The Emperor of All Maladies, Fourth Estate (2011), page 65:

     With the pectoralis major cut off, the shoulders caved inward as if in a perpetual shrug, making it impossible to move the arm forward or sideways.

• pectoralis major on Wikipedia.Wikipedia