The posterior triangle of the neck is bounded by the sternocleidomastoid muscle anteriorly and the trapezius muscle posteriorly. It is subdivided into the occipital and subclavian triangles by the omohyoid muscle. The posterior triangle contains nerves like the accessory nerve and branches of the brachial plexus, blood vessels like the external jugular vein and subclavian artery, and lymph nodes. Knowledge of the anatomy of the posterior triangle is important for procedures like brachial plexus blocks and catheterization of the external jugular vein.