Cat Ear Anatomy – Henry’s Pocket – Why it Exists

Despite every source of information that I can find reporting that the feline cutaneous marginal pouch (Henry’s Pocket) has no known use or it has no use, my theory is that this interesting piece of cat ear anatomy enhances high frequency sound detection in order to more successfully locate the cat’s primary prey, mice and other rodents, which produce ultrasound (high frequency sounds).

Feline cutaneous marginal pouch (Henry's Pocket) enhances high frequency sound detection

Feline cutaneous marginal pouch (Henry’s Pocket) enhances high frequency sound detection

There is nothing on the internet or the books I have which informs me why this strange pouch on one side of the ear flap exists so I have worked out a possible reason.

My curiosity was prompted by an email I received from Gene Sordillo:

Last year Philippa Jane Brown asked a question about the function of an external part of the cat’s ear. I have the same question about the small pouch located on the rim of the ear just at the base where the ear canal begins. It must have something to do with hearing, obviously, but is it possibly a device to amplify higher pitched sounds? My curiosity is getting the better of me. Thanks in advance.

 I agree with Gene that it does amplify higher pitched sounds and it does it by attenuating (muffling) lower pitched sounds so the higher pitched sounds stand out.

How do I arrive at this conclusion, which is unsupported by science and I could well be wrong?

We know that some sound entering the ear hits the ear canal leading to the ear drum more or less direct while other sound waves bounce off the ear flap. This means some sound waves are delayed before impinging upon the ear drum. Sound entering Henry’s Pocket is further delayed because is bounces around the pocket before exiting.

This delay causes interference with other frequencies – interference effects – which attenuates the loudness of some frequencies of sound – “[the ear’s] geometry leads to interference effects that attenuate other frequencies” (source: – Psychoacoustics of Spatial Hearing).

This is called a “pinna notch” meaning, I believe, that at a certain wavelength there is a blip in the sound (“pinna” refers to the ear flap, the bit you see).

The interference and subsequent reduction in the loudness of certain sounds leads to the accentuation of other sounds, namely high pitched sounds made by rodents thereby enabling the cat to detect with great precision the location of prey even when it cannot be seen. This aids survival, the reason for all evolution.

The cat has superb hearing and can hear frequencies as high as 65,000 cycles per second (or higher) a full octave and half higher than people. It is said that cats can detect frequencies from 55 Hz up to 79 kHz. Young mice emit alarm calls at 40 kHz while adult rats emit ultrasonic calls at 22 kHz 50 kHz, both detectable by cats.

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Cat Ear Anatomy – Henry’s Pocket – Why it Exists — 17 Comments

  1. Further observations on cat’s hearing. Last year I was adopted by an older Russian Blue stray who tested positive for FIV. A few months after becoming an inside cat he lost his sight. He was able to get along very well after learning the geography of the house but even changing things did not phase him. He just went slower around the new objects. To encourage him to play I used a willow twig and would tap it on the floor in front of him. He totally ignored it if it was too far away but get within reach and he was able to locate it and, with one sweep of his paw, convey it directly to his mouth. I’m convinced that, given a large enough mouse population he could have survived outside. Unfortunately he left last week to be met later at the Rainbow Bridge where I’m sure he’s currently impressing the others with his skills.

  2. I came to the same conclusion independently starting about a year ago. I am convinced the “pouch”detects and directs sounds we cannot hear.

    • Thanks for agreeing. I decided upon this theory without any input from any source so it is nice to hear from you. Thanks for visiting and commenting.

  3. Yea amazing it be true i would say. I’m amazed how a cat or kitten can be dead asleep and as soon as can opener or cat biscuits etc and hes or shes there. Yes i reackon the same about Radors.

  4. Amazing! I’ve often wondered about that little pouch 🙂 Its fascinating isn’t it? I always think cats ears are like little radars the way they move about, prick up and twitch! They are so sensitive.

  5. Fascinating! I’m always amazed at how a cat can hear a mouse long before it can even be seen. We’ve seen both Walter and Jozef suddenly alert, run down the garden through the little tunnel to the other side of the fence and return moments later with the mouse which was taken by surprise in the undergrowth of the trees.
    It could well be ‘Henry’s pocket’ picking up the sound.
    Cats are amazing!

      • It’s strange how they accept the sounds of Nature too, dogs barking and whining don’t seem to bother them at all, yet they drive us mad. Loud music too, the boom boom type, cats just sleep through it while we are wide awake and irritated. It’s as if cats are attuned to only what they want and need to hear, when they know they are in a safe place.

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