atlanto-axial

The first part of the movement is an eccentric or asymmetrical one; the atlanto-axial joint of the side to which the head is moved is fixed, or practically fixed, by the muscles of the neck, and forms the center of the movement, while the opposite atlantal facet is carried downward and forward on the corresponding axial facet.

III. Syndesmology. 5b. Articulation of the Atlas with the Epistropheus or Axis 1918

"With regard to the loss of voluntary movement of the ears in man and monkey, may I ask if you do not think it might have been caused, as it is certainly compensated, by the facility and quickness in turning the head, possessed by them in virtue of their more erect stature, and the freedom of the atlanto-axial articulation?

More Letters of Charles Darwin — Volume 2 Charles Darwin 1845