pectoralis minor

pectoralis minor (plural pectoralis minors or pectorales minores)

1. The muscle that covers the heart organ.
   • 2010, Siddhartha Mukherjee, The Emperor of All Maladies, Fourth Estate (2011), page 64:

     Halsted had seen Volkmann remove not just the breast, but a thin, fan-like muscle spread out under the breast called the pectoralis minor.

• pectoralis major
• pectoralis

• Merriam Websters 3rd Revised Dictionary