and the accessory process. The costiform is lateral, the mammillary is superior (cranial), and the accessory is inferior (caudal). Structurally, the mammillary process arises as a distinct bony tubercle from the posterior aspect of the superior articular process, serving as an attachment site for the multifidus muscle. The accessory process is situated at the back part of the base of the transverse process. The tallest and thickest costiform process is usually that of L5.

First and fifth lumbar vertebrae