Transversus Thoracis Muscle:

• These muscles originate from the posterior surface of the inferior sternum and attach to the internal surface of the costal cartilages 2 to 6

• They act to weakly depress the ribs

• They are innervated by T2 to T6 intercostal nerves
  

Pectoralis Major

• This muscle originates at the anterior surfaces of the medial half of the clavicle, the sternum, and related costal cartilages and the muscle fibers converge to form a flat tendon, which inserts into the lateral lip of the intertubercular sulcus of the humerus. Pectoralis major adducts, flexes, and medially rotates the arm.

• It acts to flex, adduct, and rotate the humerous, and to keep the arms attached to the trunk
  

• It is innervated by the medial and lateral pectoral nerves

Pectoralis Minor:

• This originates from the margins of the third to fifth ribs and attaches to the medial border and superior surface of the coracoid process of the scapula

• It acts to stabilize the scapula by pulling it downwards and anteriorly against the thoracic wall

• It is innervated by the medial and lateral pectoral nerves