The spinous process of a vertebra, directed backward and downward from the junction of the laminae (in humans), and serves for the attachment of muscles and ligaments
Posteroinferiorly extends from the top of the vertebral arch
No it doesn't. The atlas is the first cervical vertebra and the only one with no spinous process.
In the cervical spine, the C2-C6 vertebrae generally have bifid spinous proceses.
to provide a point of attatchment for muscles and ligaments