2.1. Introducing the Muscles of the Thorax

The Main Groups of Thoracic Muscles

There are three main groups of thoracic muscles:
  • The intercostal muscles, which lie in-between the ribs in the intercostal spaces. These are named depending on how deep they lie, i.e. they are called the external, internal and innermost intercostal muscles.
  • The diaphragm. This is a muscular sheet with two domes and a central tendon. It is the main muscle used in normal, quiet breathing. It also marks the inferior boundary of the thoracic cavity.
  • 'Assisting' muscles in respiration, namely serratus anterior, serratus posterior, pectoralis major, pecotralis minor, subclavius and the scalene muscles.
These muscles are only used during forced inspiration or expiration.