Membranous can describe things resembling a membrane, not just actual biological membranes.

Not Always Literal

Used metaphorically, 'membranous' can imply something is fragile or easily broken.

Metaphorical Use

The term often conveys a visual texture, suggesting transparency and thinness.

Visual Texture

In scientific contexts, 'membranous' precisely refers to structures like or relating to a membrane.

Biology Context

'Membranous' can imply a barrier which is not solid, often permitting the passage of substances.

Physical Barrier

 because that's the only living animal with one single hyper-elongated digit and then with the discovery of ichi which was far more complete and also onto genetically more mature so like closer to adulthood than these earlier specimens they actually discovered that that elongate digit was to support a membranous wing kind of like bats or

Reimagining Dinosaurs PIPE...

 right on the top surface of the limb. And you can see it right here. It just looks like a saddle you'd put on a horse. It's a very beautiful structure. And it's surrounded by membranous areas. And those membranous areas suggested to me that maybe this is some kind of dynamically flexible structure.