Model showing the location of the facial and neck muscles. The muscle bundles around the eyes and mouth are also known as the muscles of facial expression because of their function. In the neck the sternocleidomastoid and trapezium muscles are clearly seen. The former has a cylindrical shape and runs obliquely from the posterior lower part of the cranium to the anterior part of the collar bone; it controls the movement of the mandible. The trapezium has a triangular shape and extends over the back of the neck; it controls the position of the shoulder blade during active use of the upper limb. The parotid gland is seen at centre close to the ear.