We studied the trigeminal nerve in the middle cranial fossa in 20 cadaveric specimens (10 fixed skull base). Specifically, we analysed the relationships among the gasserion or trigeminal ganglion (herein referred to as the gasserion ganglion), the internal carotid artery, and the petrous bone. The dimensions of the trigeminal ganglia, the length from the ganglia to the exit foramina, and the width of the ophthalmic, maxillary, and manidibular nerves were also studied. The foramina of the middle cranial fossa were measured for their diameter and their distance from each other. Our paper compares our study to previous studies and the measurements taken in those studies. The lesions affecting the ganglion and the nerves are discussed and the surgical approaches to the middle cranial fossa, the petrous bone, and the upper clivus are also reviewed.