C1 is called the atlas. It supports the head and is named for the Greek god Atlas who was condemned to support the earth and its heavens on his shoulders. (Because the god Atlas often adorned maps, a compilation of maps came to be known as an atlas).
C2 is called the axis because the atlas rotates about the odontoid process of C2. The joint between the atlas and axis is a pivot that allows the head to turn.
C7 is sometimes called the prominent vertebra because of the length of its spinous process (the projection off the back of the vertebral body).