[M. A. Baron's concept of subarachnoid communications of the pia mater of the cerebral hemispheres].

In the pia mater of the human cerebral hemisphere certain specific structures named subarachnoid alveoli have been revealed. The best method for their revealing is the method of volumetric microscopy--tracheoscopy--but they can be detected in histological sections, as well. The subarachnoid alveoli are situated in the subarachnoid space between liquor canals. By their form they resemble honeycombs. Their walls have a carcass consisting of argyrophile and collagenous fibres to give the alveoli a definite form. The carcass is lined with arachnoid-endothelial cells. The alveoli are connected with the liquor canals by means of holes in the walls of the canals. The subarachnoid alveoli are connected with each other by means of holes in their walls. The arachnoid-endothelial cells of the subarachnoid alveoli are capable to accumulate colloid substances from the spinal liquor. The walls of the subarachnoid alveoli discharge macrophages into the lumen of the latter. Protective function of the subarachnoid alveoli system contributes to normalization of the spinal liquor composition both under normal and pathological conditions.