Sunday 13 July 2014

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

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

Have you noticed that rather strange secondary ear flap attached to the main ear flap (the bit you see) in your cat? If you look carefully you see what is described as a "pouch" or "pocket" at the lower part of the ear flap (scientific name: pinna). The photo shows it:

Everyone says that this pouch or pocket serves no purpose. I disagree - but cautiously - because I am not sure. However, it is a part of the anatomy of a cat's ear and nature wouldn't have allowed it to evolve without a reason, I believe.

All evolution is about survival. I therefore concluded that Henry's Pocket or the "feline cutaneous marginal pouch" (as it is scientifically referred to) exists to enhance hearing of high frequency sound produced by its primary prey: the mouse.

The only reason for enhancing hearing is to improve the chances of survival which can be translated into improving the chances of catching prey. Domestic cats are wild at heart.

Therefore having researched "pinna notch" I concluded its presence was a modification of that. What is pinna notch?

It is the inference and consequential reduction in strength of sound waves of a certain frequency as they hit the ear drum because some sound bounces around the ear before entering the ear canal and impinging upon the ear drum, while some sound enters the ear drum direct. The later is a direct path and the former is the longer path. The sound that has the longer path interferes with sound of a different frequency which takes the shorter path causing it to be attenuated (reduced in volume). Henry's pocket creates an area where sound bounces around before exiting to the ear drum at the end of the ear canal.

This allows high frequency sound to stand out more and become more noticeable, which aids the cat in detecting the sounds that rodents make which are high pitched (ultrasound).

That is the theory and it is only a theory. The link at the top of the page takes you to a similar article which explains it differently! It is a rather complicated theory. No one else has proposed this.

Cats have better hearing than dogs and much better than ours. There range of hearable frequencies is much wider. Cats are superb at detecting and locating rodents through sounds.

Note 1: please see the comment: Anonymous 16 January 2016 at 07:15 which provides a very credible reason for the existence of this anatomical ear feature.

Note 2: this is a cross-post because I think the idea deserves to be posted on more than one website.


  1. Dogs also have this pocket.

    1. Thanks TJ for that. Dogs have enhanced hearing too so I guess this mysterious bit of anatomy does something similar for dogs.

  2. Michael,
    Your observations are very good, however they not quite correct because you are mixing up the concept of 'longer paths' with 'longer frequencies'.
    What happens in fact (and this has been well studied in humans) is that, as you observed, an incoming sound wave (of whatever frequency) impinges directly on the eardrum. Simultaneously the same sound wave, again as you observe, bounces off the tragus (Henry's pocket) and it's folds, taking a longer path to the eardrum. However we are still talking about the same frequency, as it is not the wavelength that changes but rather the time it takes for those waves to get to the eardrum. In other words: as the sound bounces off the pina and tragus it is delayed.
    So then it is the difference between the first arriving wave that directly hits the eardrum, and the subsequent ones delayed by the tragus, which creates a phase (not frequency) difference within the ear.
    This then works in conjunction with the fact that we (and our cats) have two ears, just like we have two eyes, and so we/they have binaural hearing just like having binocular vision. In other words: having two ears allows us to have stereo hearing just as having two eyes allows us stereo vision (seeing in 3D).
    This means then that the structure of our feline friends ears (as well as other animals, most notably owls) gives them an ability to 'localize' sound (knowing where they are coming from in 3d space) much better than us.

    As for them being able to hear frequencies higher than we do? That's not so much about the structure of the outer ear as it is the inner ear and it's attached nervous system.

    So Yes our fuzzy friends not only hear but localize (know physically in space) where that mouse is long before we do!

    1. Thanks a lot for a great comment which is very credible. I may well use it to do a follow up article or amend and add to this one. I don't know of any other article on this subject which explains it like your comment.

  3. Good article, Michael, as is the comment from Anonymous, but neither of you address why it's called "Henry's Pocket". I'm curious about that. Any information?

    1. Another challenge! I'll try and find out. It must be a guy called Henry - a scientist perhaps - who first discussed it and proposed reasons why it exists. That said the reason why I came up with my suggestion is because I could find nothing on it.

  4. I have parked my 26 year old Oldsmobile in the garage because I am waiting for it to evovle into a Corvette, becauase nature knows I need to go faster!


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