It usually refers to membranous structures that line or cover particular organs.

The aponeurosis of the obliquus externus abdominis is a thin but strong membranous structure, the fibers of which are directed downward and medially.

However, the body feathers of Epidexipteryx are unique in that some appear to arise from a "membranous structure" at the base of each feather.

The anal, caudal, and two dorsal fins are fused together with membranous structures, forming a continuous margin around the posterior of the body.

The nuclear envelope is a membranous structure containing large protein complexes supported by a network of nuclear lamins.

It is found in discrete convoluted, vesico-tubular membranous structures in the erythrocyte cytoplasm.

They are unique in that some appear to arise from a "membranous structure".

False ribs are interconnected membranous structures that are connected with the sternum process.

Magnetosome chains are membranous prokaryotic structures present in magnetotactic bacteria.

Their two dorsal fins are connected by a membranous structure and their eyes are highly reduced.