The levatores costarum (Latin: musculi levatores costarum) are a group of 12 pairs of muscles located in the posterior thorax. They are located on each side of the vertebral column and stretch between transverse processes of vertebrae and ribs found one level below. These muscles lie superficially to the external intercostal muscles.
The levatores costarum are considered as intrinsic muscles of the chest wall, as well as one of the deep muscles of the back. Together with other thoracic muscles, they possibly play a role in forced respiration and preventing the chest from moving inwards during inspiration. Along with the interspinales and intertransversarii muscles, they form the fourth (deepest) layer of the deep back muscles, participating in movements of the spine.
The levatores costarum arise from transverse processes of the seventh cervical to eleventh thoracic vertebrae (C7 - T11). Each muscle originates from one transverse process and passes obliquely downward.
Each muscle inserts into the superior border or external surface of a rib one level below its origin. To be more precise, the insertion site is between the costal angle and the tubercle of a rib.
Each levatores costarum muscle is triangular-shaped, with the base at its insertion and the apex pointing toward the origin. The upper eight muscle pairs appear as single muscular bands, while the lower four split into two fasciculi - a long and a short fasciculus. These two bundles are called levatores costarum longi and levatores costarum breves, and both have a common origin site. The short (breves) fascicles insert into the ribs one level below their origin, while the long (longi) fascicle descends further and attaches to the rib located two levels below.
The functions of the levatores costarum include elevating the ribs and producing rotation and lateral flexion of the thoracic spine. Although these muscles can elevate ribs, they are thought to play a relatively unimportant role during inspiration.
Lateral branches of the dorsal rami of the spinal nerves C8 - T11 (intercostal nerves) innervate the levatores costarum muscles.