It arises from the trigeminal ganglion, runs forwards in the lateral wall of the cavernous sinus below the ophthalmic nerve, and leaves the middle cranial fossa by passing through the foramen rotundum. Next, the nerve crosses the upper pa of the pterygopalatine fossa. In the pterygopalatine fossa, the nerve is intimately related to the pterygopalatine ganglion and gives off the zygomatic and posterior superior alveolar nerves. The posterior superior alveolar nerve enters the posterior surface of the body of the maxilla and supplies the three upper molar teeth and the adjoining pa of the gum.Ref: BD Chaurasia&;s HUMAN ANATOMY, Volume 3, 6th edition.