Upper Two Vertebrae
The upper two vertebrae of the spinal column, involved in head movement. In performing the rotary motion of turning your head, the skull does not move alone, but it moves together with the first vertebra. The first vertebra in this motion moves on the second around a tooth-like process that stands up from this second vertebra. This tooth works in a smooth notch on the inside of the first vertebra. It is bound very fast in this notch by a strong ligament, so that it may not, in any of the quick motions of the head, be made to press on the delicate spinal marrow which lies against it.