<prompt> Most impoant muscle which opens mouth isLateral pterygoidMedical pterygoidMasseterTemporalis  <response>: The lateral pterygoid may be regarded as the key muscle of this region because its relations provide a fair idea about the layout of structures in the infratemporal fossa. the relations are as follows: Superficial 1.masseter 2.Ramus of the mandible 3.Tendon of the temporalis 4.The maxillary aery Deep 1.mandibular nerve 2.middle meningeal aery 3.Sphenomandibular ligament 4.Deep head of the medial pterygoid 