The internal plate of the dura mater and arachnoidea of the dob brain was studied by electron microscopy after introducing 0.3--0.5 ml of the autogenous blood into the subdural space. The arachnoidea of the excretory channels and structural elements of the internal plate of the dura mater (cells of the internal covering layer, the collagen fibril and microfibril layer, the wall of the blood capillaries of the internal capillary network) involve the morphological substratum of the liquor-blood barrier-I between the liquor and blood of the blood capillaries of the internal capillary network of the dura mater. It was established that red cells of the subdural space penetrate the thickness of the dura mater, where they concentrate around blood capillaries of the internal capillary network, rather than penetrate into the arachnoidea.