The anterior skull base from the transcranial view. The planum (or jugum) sphenoidale is a flat surface on the upper aspect of the sphenoid bone that connects the two lesser wings. The limbus of sphenoid bone is a prominent ridge on the body of the sphenoid forming the posterior border of the planum sphenoidale and the anterior border of the prechiasmatic sulcus. The prechiasmatic sulcus is an osseous groove that runs transversely between the optic nerves. The sphenoid sinus lies underneath the planum sphenoidale. The crista galli and cribriform plate are anterior to the planum. (Image courtesy of JC Fernandez-Miranda)