Deepest layer of deep cervical fascia is
Prevertebral
Carotid sheath
Pretracheal
Temporal
Deep cervical fascia, also known as fascia colli is condensed to form 6 layers.

Investing layer.
Pretracheal layer.
Prevertebral layer.
Carotid sheath.
Buccopharyngeal fascia.
Pharyngobasilar fascia.

Prevertebral fascia:

It is the deepest layer of deep cervical fascia.
It lies in front of prevertebral muscles and forms the floor of posterior triangle of neck.
It is separated from pharynx and buccopharyngeal fascia by retropharyngeal space.