# What's the purpose of the double flap on a dog's ear? **URL:** \ **Category:** Factual Questions\ **Created:** [June 9, 2001, 9:50pm UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212 "2001-06-09T21:50:36Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [June 9, 2001, 9:50pm UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/1 "2001-06-09T21:50:36Z")
Although I’ve not done a scientific survey, most dogs have a little double flap, or double layer of skin, on one side of their ear, the side closer to the ground. What’s the purpose of that little flap? just a quirk of evolution? ---
**Author:** ![rjk](https://avatars.discourse-cdn.com/v4/letter/r/ed655f/32.png) [@rjk](https://boards.straightdope.com/u/rjk)\ **Post date:** [June 10, 2001, 1:36am UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/2 "2001-06-10T01:36:40Z")
I think I know the bit you’re talking about. I don’t know much about dog ears, but it might be involved in locating the direction of sounds. Ear shape modifies the sound you hear according to its direction, as it reflects off the convolutions. Take a look at [http://www.sfu.ca/sca/Manuals/ZAAPf/b/binaural\_local.html](http://www.sfu.ca/sca/Manuals/ZAAPf/b/binaural_local.html) for a brief description, or [http://www.binaural.com/binfaq.html](http://www.binaural.com/binfaq.html) for more than you wanted to know about synthesizing sound-position info. Or maybe it _is_ just a quirk. ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [June 10, 2001, 1:38am UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/3 "2001-06-10T01:38:01Z")
In this thread [http://boards.straightdope.com/sdmb/showthread.php?threadid=30964](http://boards.straightdope.com/sdmb/showthread.php?threadid=30964) I said > [@](#): > > Are you talking about what I think you’re talking about? A pouch-like structure on the edge of the ear? If that’s not what you’re talking about, you can ignore what follows. I couldn’t find an anatomical atlas of the cat (“map of a cat” as R. P. Feynman would say) that considers this important enough to mention, but dogs appear to have more or less the same thing. The book Canine Anatomy: A systematic Study by Donald R. Adams (1986) says (pp 12-14), > > ## quote: > > ## A cutaneous marginal sac of unknown significance occurs in the antitragic margin. > > If the anatomist doesn’t know what it’s for, I’m not going to speculate. I have scanned the accompanying diagram and you can see it [here](http://msnhomepages.talkcity.com/LibraryLawn/bibliophage/pinna_canis.html). I have underlined “cutaneous marginal sac” in red, since it’s hard to read ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [June 10, 2001, 2:13am UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/4 "2001-06-10T02:13:51Z")
**bibliophage** , that’s what I meant - thanks. As you say, if the anatomy profs don’t know… **rjk** , I’m not sure that it would affect the dog’s ability to hear, because it’s found on dogs with pointy-up ears (like in the illustration bibliophage posted), and also in floppy hang-down ears (like beagles and bassets). Although it’s located in the same anatomical region of the ear in both cases, I would think that the different physical location would mean that it would not have the same effect on the dog’s ability to hear. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [June 10, 2001, 4:10am UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/5 "2001-06-10T04:10:56Z")
If the anatomy profs don’t know, you can’t look it up, so you have to figure it out for yourself. ## Cats and dogs apparently diverged from their common ancestor (Miacis) 30 or 40 million years ago. That seems like a **very** long time for such a complex structure to hang around if it were just a quirk of evolution. If you grab a handy cat, or dog ?, and pull the back of their ear directly away from the head, you’ll see that the structure stretches like a spring, (or a folded piece of paper when pulled). The stress exerted by pulling on the ear also looks to be more spread out with the flap thing, than it would be if the ear were more simply constructed. So maybe the flap helps prevent torn ears during fights etc. ? For a cat ancestral tree see: [http://dspace.dial.pipex.com/agarman/bco/prehistoric.htm](http://dspace.dial.pipex.com/agarman/bco/prehistoric.htm) A Google search on “Miacis”, “prehistoric cat” or “prehistoric dog” turns up scads of interesting stuff. ---
**Author:** ![Northern\_Piper](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/northern_piper/32/5304_2.png) [@Northern\_Piper](https://boards.straightdope.com/u/Northern_Piper)\ **Post date:** [October 1, 2025, 10:58pm UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/6 "2025-10-01T22:58:55Z")
I asked this question 24 years ago and got a “no-one seems to know” answer, as set out above. Today, 24 years on, through the miracle of Wikipedia, I discovered an article on this very topic! The answer? “No-one seems to know”. But, at least there’s a name for it! I give you: > **[Henry's pocket](https://en.wikipedia.org/wiki/Henry%27s_pocket)** > > In animal anatomy, Henry's pocket, more formally known as a cutaneous marginal pouch, is a fold of skin forming an open pouch on the lower posterior part of the external ear. The pocket is situated in the approximate location of the antitragus in the human ear. It occurs in a number of mammalian species, including weasels and bats, but is particularly noticeable on the domestic cat, as well as some dog breeds. > It is unknown where the name "Henry's pocket" came from. The earliest known use of the... But why? Why “Henry’s pocket”? Answer: “No-one seems to know.” But at least we now know that it’s not restricted to dogs and cats. Bats have Henry’s pockets, too! Check back in, in 2049, for the next update! ---
**Author:** ![ricepad](https://avatars.discourse-cdn.com/v4/letter/r/b38774/32.png) [@ricepad](https://boards.straightdope.com/u/ricepad)\ **Post date:** [October 1, 2025, 11:01pm UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/7 "2025-10-01T23:01:02Z")
It’s the perfect size on most dogs to insert your finger and annoy your dog. Form follows function! ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [October 2, 2025, 5:18pm UTC](https://boards.straightdope.com/t/whats-the-purpose-of-the-double-flap-on-a-dogs-ear/68212/8 "2025-10-02T17:18:03Z")
I had heard it is the canine variation of the human earlobe. Which, if true, doesn’t answer your question.