OMPLICATIONS or failure in the treatment of carotid cavernous fistulas with cervical or combined cervicalintracranial carotid ligation 4-6,9,~~ have mainly been due to the presence of the collateral circulation of the internal carotid artery, namely, the cerebral communicating branches, the ophthalmic artery, or branches of the cavernous carotid segment. 9,~~ The intraluminal embolization method of Brooks, ~,z advocated by Lang and Bucy, 8 is simple and effective but has not been used widely because of the fear that the muscle or its fragments may pass into the cerebral circulation and obstruct the distal arterial segment. The possibility of this complication led many surgeons *,~3,~4 to clip the internal carotid artery intracranially before embolization. This procedure itself was not always simple or without risk. 7,8 Since there has been no report on definite complications in patients treated by embolization, its failure 4,~,~ seems to be due to the use of improper muscle embolus. However, Wanissorn, et al., ~7 using a muscle embolus slightly larger than the caliber of the common carotid artery alone, cured four consecutive cases of carotid cavernous fistula. The purpose of this investigation was to study the mechanism of muscle embolization of the carotid-cavernous fistula and the fate of emboli, particularly the role of intracranial ligation of the internal carotid artery. Experimental Method The experiments were carried out on 48 autopsied human cadavers, within 18 hours after death, aged between 10 and 68 years. The brains were removed, leaving the intracranial carotid arteries as long as possible; the dura mater over the cavernous sinus together with related cranial nerves and sur