Wordplay Wednesday: Atlas and Axis
Two of the biggest advances in tetrapod evolution was the addition of two very special cervical (neck) vertebrae: the atlas and the axis. These came with a group called amniotes.
You might be wondering why two little verts could be such a big advancement. The atlas and axis are the first two vertebrae in the cervical sequence. The atlas (C1 if you will) holds up the skull just like the titan Atlas holds up the Earth in Greek mythology.
The atlas allows us to nod our heads up and down.
The axis (or C2) is the next in line. This vertebra allows us to turn our heads from side to side.
In other words, these two little vertebrae give us an incredible range of motion that amphibians and fish lack. Take a look at their skull attachments:
Fish and amphibians have to turn their entire body in order to look in a different direction while other vertebrates can simply spin their heads on their very special cervicals. Neat, huh?