The eye begins to form during the 22nd day of embryogenesis. According to Raybaud’s developmental stages of the intracranial vascular system, the embryo is around 16–21 mm long toward the end of week seven (stage 5) and both the choroid plexus and arteries form at this time. During the seventh and eighth week of embryogenesis, the pro-otic sinus (eventually called the cavernous sinus) forms via the union of the middle dural plexus and the anterior region of the primary sinus (Raybaud 2010).