Which anatomical structure is located posterior to the medial border of the sternocleidomastoid muscle?

The common carotid artery is positioned posterior to the medial border of the sternocleidomastoid muscle. This anatomical relationship is significant as the sternocleidomastoid muscle serves as a landmark in the neck region; it divides the neck into anterior and posterior triangles. The common carotid artery, which bifurcates into the internal and external carotid arteries, runs in close proximity to this muscle, lying deep to it and more medially along the neck.

Understanding this positioning is crucial, especially in clinical practices relating to procedures involving the neck, such as surgical interventions or vascular assessments, where precise knowledge of anatomical locations is necessary for safety and efficacy. The other structures mentioned, while they might be nearby, do not share this specific anatomical relationship with the sternocleidomastoid muscle.