The meningeal layer lays over the spinal arachnoid mater. This leads to elevated intracranial pressure, cerebral edema, meningeal irritation, and neuronal death. The other two meningeal layers are the arachnoid mater and the pia mater. The meningeal lymphatics also carry immune cells. The tensor tympani receives blood from the middle meningeal artery via the superior tympanic branch. An injured middle meningeal artery is the most common cause of an epidural hematoma. Its sympathetic root is derived from the plexus on the middle meningeal artery. Very rarely the ophthalmic artery may arise as a branch of the middle meningeal artery. The anterior branch of the middle meningeal artery runs beneath the pterion. The anterior division of the middle meningeal artery runs underneath the pterion. Many of these injuries are associated with lacerations of the middle meningeal artery. Although rare, meningeal carcinomatosis can arise from cervical cancer. In approximately half of subjects it branches into an accessory meningeal artery. It is a branch of the middle meningeal artery. Speculation has included "delirium tremens", heart disease, epilepsy, syphilis, meningeal inflammation, cholera, and rabies.