The cavernous sinus was studied on 23 cadavers, 37 sinuses in total. Twelve sinuses were frozen to -150 degrees C using liquid nitrogen and cut in the middle portion to study macroscopically the whole interior structure of the sinuses. Remaining 25 were fixed 10 per cent Formalin and their serial sections were stained with Hematoxylin and Eosin for microscopic examination. The lateral wall of the cavernous sinus consists of an outer layer of dense connective tissues and an inner layer of loose connective tissues. The third, fourth and fifth cranial nerves run through the lateral wall without exception, but the sixth cranial nerve was found in the lateral wall in only 48 per cent of the specimens. The internal carotid artery is surrounded by the venous sinus all over in 72 per cent of the studied cavernous spaces. The inner surface of the venous sinus is covered with endothelial cell layers. The size and shape of the venous sinuses vary considerably, but they can be divided into three major groups; (1) the broken (58 per cent) or 2) the unbroken (33 per cent) according to amount of trabeculae and 3) the small scattered venous channels without trabeculation (9 per cent).