[Paravascular structures of the major arteries of the cerebral hemispheres (electron microscopy study)]

The ultrastructure of the paravasal formations of the magistral arteries in the brain hemispheres has been studied: the paravasal nerve trunks (components of the external nerve plexus of the arteries, running outside the adventitia and surrounded with liquor) and the artery-stabilizing constructions--strings in the human being and in the dog. The human para-arterial nerve trunks possess the vasa nervorum system, presented by blood capillaries situating at the border of endo- and perineurium, by powerfully developed perineurium, which includes into its composition a system of basal membranes and perineural cells. In the canine para-arterial nerve trunks these formation are absent. In the string composition there are collagenous-fibrillar base represented by tightly packed fasciculi of collagenous fibers, oriented in parallel to the long axis of the string, and by stellate cells. Both the paravasal nerve trunks and the strings are surrounded with flattened cells of the endothelial sheath. They are very much alike with the arachnoidendothelial cells lining the subarachnoidal space.