False about sternocleidomastoid?

Sternocleidomastoid tsternomastoidlOriginThe, sternal head The clavicular head InseionIt is inseed :By a thick tendon into the lateral surface of mastoid process, from its tip to superior border.By a thin apponeurosis into the lateral half of the superior nuchal line of the occipital bone. Nerve supplyThe spinal accessory nerve provides the motor supply. It passes through the muscle.Branches from the ventral rami of C2 are proprioceptive.Blood supplyAerial supply-one branch each from superior thyroid aery and suprascapular aery and, two branches from the occipital aery supply the big muscle.Veins follow the aeries.Actions1. When one muscle contracts :a) It turns the chin to the opposite side.b) It can also tilt the head towards the shoulder of same side.2. When both muscles contract together :a) They draw the head forwards, as in eating and in lifting the head from a pillow.b) With the longus colli, they flex the neck against resistance.c) It also helps in forced inspiration.