atlantion

A New Latin Dictionary by Charlton T. Lewis Ph.D. and Charles Short, LL. D.

ā̆tlantĭon, ii, n. [Atlas],

the lowest vertebra of the neck (so called because on it rests the whole burden of the head and the remaining vertebrae of the neck): hunc spinae articulum sive nodum Atlantion vocant, Plin. 28, 8, 27, § 99.