The longissimus muscle forms the major portion of epaxial muscle mass. It extends of the entire length on the back and neck, from the pelvis to the head, thus forming the longest muscle of the body.
Its original segmental arrangement is still reflected in the numerous individual attachments of its segmental muscle bundles. Its overlapping fascicles arise form the sacrum, ilium, the mamillary and spinous processes of the thoracic and lumbar vertebrae and run cranioventrally and laterally to insert with several tendons on the mamillary and spinous processes and the longissimus tuberosities of the ribs.
It is subdivided into: