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, and to it the galea aponeurotica is attached.

• Below the highest nuchal line is the superior nuchal line. To it is attached the Sternocleidomastoid muscle, Occipitalis muscle, and Splenius capitis muscle.

• From the external occipital protuberance a ridge or crest, the median nuchal line, often faintly marked, descends to the foramen magnum, and affords attachment to the ligamentum nuchæ.

• 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.