Anterior Genu and Anterior Vertical Segments of Carotid Artery. G and H, Transmaxillary exposure of the anterior genu and anterior vertical segment. G, The posterior wall of the maxillary sinus has been opened and the approach directed through the pterygopalatine fossa and above the vidian nerve through the lateral part of the sphenoid sinus to access the anterior genu and anterior vertical segment. Branches of the maxillary artery and second trigeminal division are exposed in the pterygopalatine fossa. H, Endoscopic view. The vidian nerve has been followed back to where it joins the greater petrosal nerve, which courses on the upper surface of the horizontal segment of the petrous carotid. The posterior trigeminal root and ganglion and third division are in the lateral margin of the exposure. The petrous apex is exposed posterior to the petrous carotid. Bundles of the carotid neural plexus ascend on the petrous carotid. I and J, View of the anterior genu and anterior vertical segment through a transcranial transbasal exposure. I, A bifrontal bone flap has been elevated and the posterior part of the floor of the anterior fossa has been removed to expose the sphenoid sinus. The vidian nerves, which can be followed backward to the petrous carotid, underlie prominences in the floor of the sphenoid sinus. An osteotomy has been completed around the cribriform plate. J, The walls of the sphenoid sinus have been removed to expose the cavernous segment and the anterior vertical segment and anterior genu of the petrous carotid. The vidian canals have been unroofed to expose the vidian nerves in the floor of the sphenoid sinus. (Images courtesy of AL Rhoton, Jr.)