Detaching the trapezius and sternocleidomastoid muscles, as the most superficial muscle layer, we can find the second muscle layer composed by the semispinalis capitis muscle, medially, and the splenius capitis muscle, laterally. The semispinalis capitis has its source in between the superior and inferior nuchal lines, beginning in the midline, at the external occipital crest, and extending laterally to the occipitomastoid suture. (Image courtesy of E de Oliveira)