Three lines that transversely cross the cranial rear. From lowest to highest they are:

inferior nuchal line extends across the middle of the nuchal lane, separating the nuchal muscles semispinalis capitis above from rectus capitis below.

superior nuchal line the most prominent, develops along the top of the semispinalis capitis muscle and some of the muscles lying over it attach directly to the line, trapezius more centrally and sternocleidomastoid more laterally. It separates the nuchal from the occipital planes of the occiput.

supreme nuchal line lies above the superior line, on the occipital plane. It may be totally absent, a distinct line dipping downward at the midline, or the superior border of the nuchal torus (if there is one).