Case report: the cleidocervical muscle with speculation as to its origin.

The occurrence of a cleidocervical muscle, which arose from the anterior tubercle of the transverse process of the 6th cervical vertebra and was inserted onto the superior margin of the clavicle, is described. Detailed observations on its innervation, which was derived from the 5th cervical nerve, and its topographic anatomy suggest that the muscle originated from longus colli.