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There is so much going on with these two vertebrae that they get special notice..
We see three views of the neck: FRONT, SIDE, & BACK views. The neck vertebrae are numbered 1 through 7 sittine one upon the other in a stack. The top two vertebrae are unique enough for special attention.
 C1 has had it’s body stolen by C2. That stolen body persists as a upward jutting finger (shown white on right) from C2 into a recess in C1. It is said to act as a pivot for C1. On the back of that recess is a ligament (shown red).
The top of C1 has two joints which embrace the skull and support i - each shaped like fat 8’s. Because these joints support the head (like a big globe), the C1 vertebra is called Atlas.
It’s easier to confuse people if you give one thing many names and so the pivot bone from C2 jutting upward into C1 is called both the DENS and also called the ODONTOID bone or process. Why? Because before there was television and comic books there was little to distract from the plague. Lot’s of confusing names. (can make it even harder to remember if you call it the Os Odontoideum - Latin).
 So, within this ring called C1 we have the top of two pillars. The pillars actually carry the load. The top of each pillar is a joint support for what is above and at the bottom a joint for the vertebra below.
Looking at the front of C1, the yellow arrows indicate the pillar support. C1 is mostly pillars joined in a ring. C2 is much more substantial and could have been called biggy, but that pivot stands out as so unique that C2 is called AXIS.
Want to know a secret? This isn’t in print anywhere else, but it isn’t really a finger, that odontoid process (or dens). It has a very special shape that you might recognize. That shape is called a catenary - OK - a hard word... but you do know the shape, like a pair of parentheses ( ). That is the shape of a COG, the pointy things in gears that mesh with each other. Cog shape is the most efficient shape known to push using rotary motion with least friction. Hmmmm. So, while it mat be an axis for looking left and right, it is a cog for gear-like flexion-extension of the head whose center of motion is a fluid area. That puts the center of all this complex motion away from neurons in a liquid. Clever, huh? Shhhhh. Don’t tell anybody our secret.
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