nuchal line

:  any of several ridges on the outside of the skull: asa:  one on each side that extends laterally in a curve from the external occipital protuberance to the mastoid process of the temporal bone—called also superior nuchal lineb:  occipital crest ac:  one on each side that extends laterally from the middle of the external occipital crest below and roughly parallel to the superior nuchal line—called also inferior nuchal line