Scanning electron microscopic observations of the subarachnoid space were made in dogs focussing upon the fibre components in both the normal subarachnoid space and in areas of post-haemorrhagic fibrosis. It was concluded that the fibrous tissue originates from the arachnoid membrane itself, while organized haematoma is considered to form a component of the fibrosis. Perfusion of the subarachnoid space of dogs with a solution of 0.1% Toluidine Blue was also done. This showed that cerebrospinal fluid (CSF) is carried from the subarachnoid space directly to the dural sinuses through a fine string-like structure, which is conceivably one of the collateral CSF absorptive pathways.