The Pinna is the most visible parts of the Ear
Let's take a look at the segments of the ear individually, and see what the boundaries are, and what contribution is to hearing for each.
The Outer Ear: The Pinna of the Outer ear is the most visible part. It's what many folks think of as the ear. In terms of hearing, it doesn't really contribute much.
If we had Pinnas like rabbits or donkeys there might be some sound gathering and resonance benefits.
In the graphic view, you can see Diagram Figure A-15 from the text, page 394 of the Outer Ear (colors added).