Intermediate Dissection of Posterior Neck Muscles. The trapezius muscles and nuchal ligament have been removed to expose the splenius capitis muscles. These, in turn, overlie the longitudinally-oriented semispinalis capitis muscles that attach to the occipital bone between the superior and inferior nuchal lines. The occipital artery is a branch of the external carotid artery. It is shown here having passed deep to the splenius capitis and penetrating the semispinalis capitis. It normally passes through the trapezius muscle to supply the posterior scalp. (Image courtesy of PA Rubino)