The bony nasal septum is composed of the perpendicular plate of the Ethmoid Bone.

http://en.wikipedia.org/wiki/Anatomy_of_the_human_nose

Above and to the back (posterosuperiorly), the bony nasal septum is composed of the perpendicular plate of the ethmoid bone. The vomer bone lies below and to the back (posteroinferiorly), and partially forms the choanal opening into the nasopharynx, (the upper portion of the pharynx that is continuous with the nasal passages). The floor of the nose comprises the premaxilla bone and the palatine bone, the roof of the mouth.