Posterior muscles (two groups)
The inferior attachments are more lateral than the superior attachments.
Therefore, this group causes contralateral rotation*.
The inferior attachments are more medial than superior attachments.
Therefore, this group causes ipsilateral rotation * of the trunk.
Transverse plane illustration of muscles' effects on rotation. Point of application is drawn on superior vertebra. Line of application follows muscle fibers medially or laterally, depending on group, to their attachment on inferior vertebra.