visceral layer. Definitions: 1. the inner layer of an enveloping sac or bursa that lines the outer surface of the enveloped structure, as opposed to the parietal layer that lines the walls of the occupied space or cavity.he visceral layer is usually thin, delicate, and not apparently separate, but instead seems to be the outer surface of the structure itself. Synonyms: lamina visceralis. The definition information for visceral layer is provided by Stedman's.