The rectus capitis lateralis are muscles in the upper neck below the back of the head on each side. They are responsible for controlling movements occurring when the head tilts to the side. One end of the muscle attaches to the transverse process at the side of the C1 vertebra, and then travels up the side of the neck bones. The other end of the muscle attaches to the jugular process on the lower part of the cranium. The anterior primary rami of C1 and C2 provide the nerve supply to the muscle. Pain occurs deep in the neck tissue just below the base of the skull. The cervical artery brings blood to the muscle. If the C1 vertebra is out of alignment or the neck is tender in that area, a medical examination is advised. Gentle pressure on the area is enough to diagnose muscle strain. It's unlikely the doctor will locate the muscle directly, but surround tissue will push against the rectus capitis lateralis muscle alerting the patient to pain.