Lewis & Short

vertĭcŭla, ae, f. dim. [verto], a joint, = vertebra, Lucil. ap. Non. p. 207, 24; cf. Fest. p. 371.
In machines, Vitr. 10, 13, 1.
Called also vertĭcŭlus, i, m., Sol. 4; Cael. Aur. Tard. 4, 3, 242; vertĭcŭlum, i, n., id. Acut. 3, 17, 138.