Deep Cervical Fascia-Part 1

A patient was brought to the OPD with a history of psychotic episodes and a sudden twisting of the head to one side and the face to the other. On examination, he was diagnosed with a case of spasmodic Torticollis. The muscle that has gone into spasm takes its origin from the sternum and clavicle and is inserted into the mastoid process and occipital bone. Which fascia encloses this muscle?