Anatomy, Thorax, Muscles

The thoracic wall is made up of five muscles: the external intercostal muscles, internal intercostal muscles, innermost intercostal muscles, subcostalis, and transversus thoracis. These muscles are primarily responsible for changing the volume of the thoracic cavity during respiration. Other muscles that do not make up the thoracic wall, but attach to it include the pectoralis major and minor, subclavius, and serratus anterior (anteriorly) and the primary costarum and serratus posterior superior and inferior (posteriorly). The muscles of the anterior thorax provide movements to the arm and shoulder while the muscles of the posterior thorax also help change thoracic volume during breathing and reinforce the thoracic wall. The diaphragm is another muscle in the thorax that serves as the main muscle of inspiration. It also makes up the floor of the thorax, thus separating the contents of the chest from those of the abdomen. Other minor accessory muscles that attach to the thorax include the scalene muscles and the sternocleidomastoid muscle, both of which may also minimally aid in respiratory efforts.