The nuchal lines are four curved lines on the external surface of the occipital bone:

• The upper, often faintly marked, is named the highest nuchal line, but is sometimes referred to as the Mempin line or linea suprema, and it attaches to the epicranial aponeurosis.
• Below the highest nuchal line is the superior nuchal line. To it is attached, the splenius capitis muscle, the trapezius muscle, and the occipitalis.
• From the external occipital protuberance a ridge or crest, the external occipital crest also called the median nuchal line, often faintly marked, descends to the foramen magnum, and affords attachment to the nuchal ligament.
• Running from the middle of this line is the inferior nuchal line. Attached are the obliquus capitis superior muscle, rectus capitis posterior major muscle, and rectus capitis posterior minor muscle.