The orbicularis oris muscle encircles the opening of the mouth and helps to bring the lips together to keep the mouth closed. Pursing of mouth is due to orbicularis oris inseed into lips and angle of mouth supplied by VII nerve.The muscles of facial expression are innervated by branches of the facial nerve (VII). After emerging from the stylomastoid foramen, the facial nerve lies within the substance of the parotid gland. Here, it gives off its five terminal branches: (1) The temporal branch courses up to the scalp to innervate the occipito frontalis and orbicularis oculi muscles. (2) The zygomatic branch courses across the cheek to innervate the orbicularis oculi muscle. (3) The buccal branch travels with the parotid duct and innervates the buccinator and orbicularis oris muscles, and also muscles that act on the nose and upper lip. (4) The mandibular branch innervates the orbicularis oris muscle and other muscles that act on the lower lip. (5) The cervical branch courses down to the neck and innervates the platysma muscle. Ref: Dhillon N. (2012). Chapter 1. Anatomy. In A.K. Lalwani (Ed), CURRENT Diagnosis & Treatment in Otolaryngology--Head & Neck Surgery, 3e.