パンの耳? How did 耳 end up meaning edge/crust?

Question

100% a curiosity question, but I recently stumbled across some older blog posts about a silly debate of "should you eat all your pizza crust?" and I was surprised to see the phrase

ピザの耳

Most of the time when I've seen the word crust its' been クラスト or パンの皮.

So as more of an etymological inquiry, does anyone know how exactly 耳 end up meaning crust or edge?

My usual Jisho and Wiktionary sources are leaving me dry and through my own search, I could find plenty on the Chinese etymology with 耳's relation to ear. Likewise it's obvious how selvage, crust, and edge are all related, but I couldn't find anything that connects the two. Seeing as both ピザの耳 and パンの耳 are used, I'm not sure if it's something that would trace back to the introduction of (Western) breads or pizza to Japan (since who knows which usage came first) or is something as simple as 'ears are on the edge of your face'.

Answer 1

This is simply because 'ears are on the edge of your face'. The edge of a coin was also called 耳 in the past, and 耳を揃える is still commonly used as an idiom.

• 語源由来辞典 - 耳を揃える

  「耳」は頭部の中心から端に位置することから、「パンの耳」と言うように「縁」を意味する。

• なぜパンの端を耳というのか？

  そもそも日本人は、モノの端の部分を耳と表すことが多く、これはパンに限っての話ではない。例えば、布や紙の端の部分も耳と言い表すことがある。これらに共通しているのは平面的な物体という点だ。日本人は平面的なものの端の部分を耳と呼ぶのである。

_{(By the way, I didn't know this part is called "heel" by many English speakers.)}