[1] It has an irregularly quadrilateral form, broader than the serratus posterior superior muscle, and separated from it by a wide interval.

It arises by a thin aponeurosis from the spinous processes of the lower two thoracic and upper two or three lumbar vertebrae.

[citation needed] The serratus posterior inferior draws the lower ribs backward and downward to assist in rotation and extension of the trunk.

[1] This movement of the ribs may also contribute to inhalation and forced expiration of air from the lungs.

[2] This article incorporates text in the public domain from page 404 of the 20th edition of Gray's Anatomy (1918)