Thoracic wall muscles are essential for respiration. Few anatomical variations in thoracic wall muscles have been reported. Such variants must be considered during surgical procedures that involve the thorax muscles. During routine dissection of a 65-year-old male cadaver as part of a fourth-year clinical anatomy elective, additional muscle strips were found in the inner and inferior aspect of the rib cage closer to the posteromedial body wall. The muscle consisted of two strips of narrow muscle fibres originating from the inferior borders of ribs 11 and 12 that radiated to insert on the transverse processes of the T11 and T12 vertebrae. The case report describes an unusual, novel medial thoracic wall muscle that has not been previously described in the literature. Variations in thoracic muscles can affect respiratory function and surgical interventions like chest tube placement and needle therapy for local anaesthesia, therefore, it is important for clinicians to be aware of such variants.
Keywords: T11 and T12 vertebrae; anatomical variations; posteromedial wall; rare thoracic wall muscle; rib cage.