The term arachnoid (arac) refers to the middle of three meninges (men), supporting structures that surround the brain (BRN) and spinal cord (SPC) in vertebrates ( Swanson-2015 ). The arac is a fine web-like structure whose openings provide the subarachnoid space for cerebrospinal fluid (CSF). Together they cushion the BRN against a traumatic blow to the head ( Carpenter-1983 ). The arac is found in the human, macaque, rat and mouse ( NeuroNames ). Final 22 Dec 2024.