The parotid gland (see pp. 900–901) on each side is entirely outside the boundaries of the oral cavity in a shallow triangular-shaped trench (Fig. 8.264) formed by: the sternocleidomastoid muscle behind, the ramus of the mandible in front, and superiorly, the base of the trench is formed by the external acoustic meatus and the posterior aspect of the zygomatic arch.