Volume 197 - Issue 11
Cats’ ears and stethoscopes
Author: Hedley G Peach
Med J Aust 2012; 197 (11): 673. || doi: 10.5694/mja12.11570
Published online: 10 December 2012
Published online: 10 December 2012
To the Editor: I hoped that looking after cats might reduce my anxiety over retiring. That was until I spotted pouches at the base of the cats’ ears. I had to find out why cats had ear pouches.
Texts on veterinary anatomy were not helpful. I found other people had been asking the same question on the internet without much success.
Someone had suggested ear pouches ...
To the Editor: I hoped that looking after cats might reduce my anxiety over retiring. That was until I spotted pouches at the base of the cats’ ears. I had to find out why cats had ear pouches.
Texts on veterinary anatomy were not helpful. I found other people had been asking the same question on the internet without much success.
Someone had suggested ear pouches may be vestigial. That doesn’t help because vestigial structures can still have an important role. Take, for example, the appendix.1 However, I could not find a record of a functional pouch in cats’ ancestors or close relatives to support the notion of vestigiality.
Comparing one group with others often yields clues in epidemiology. I discovered that cats are not the only mammals that have pouches on their ears. Some dogs and foxes do too. All three species have large concave pinnae as well as small pouches.2 Most mammals do not have ear pouches.
It is not easy to measure the hearing of animals, but I found data on the hearing range of cats and 16 other mammals.3 Cats, foxes and dogs have the broadest hearing range of all the mammals. They hear sounds up to 43 kHz above the human range and up to 19 Hz below it. Horses and cows can hear sounds above and below the limits of human hearing but over a much narrower range than cats. Many other mammals such as rats and rabbits can hear sounds above the human range but not below it. Conversely, elephants can hear sounds below the human range but not above it.
It seems that there might be an association between the broad hearing range of cats and their large concave pinnae and small ear pouches. It is well known that cats can move their ears independently of one another to focus on where a sound is coming from. I have observed that cats’ ears often become more or less concave when cats move their ears, as if trying to home in on a particular sound. This reminded me of something I had read about the stethoscope used by William Osler. Osler’s stethoscope had a large bell into which he would screw a smaller bell when he wanted to localise low-frequency sounds during auscultation of the heart.4 Like the smaller bell of Osler’s stethoscope, the pouches on cats’ ears might enable them to localise low-frequency sounds. The Denison stethoscope (c. 1885) had three or even four progressively smaller bells.4 Perhaps cats’ small ear pouches and their ability to increase the concavity of their large pinnae serve a similar purpose to the multiple bells.
There were occasions, such as during the examination of children, when large bells on early stethoscopes were a nuisance. The Down Brothers stethoscope (c. 1900) had a large bell that could be unscrewed to create a smaller bell for children.4 The large pinnae of cats are a nuisance when squeezing through small gaps. At such times, and perhaps akin to unscrewing the Down Brothers bell, I have observed that cats flatten their ears and fold them back but above the roof of the pouch. This leaves the pouch exposed, open and able to pick up sound.
Veterinarians may have a new line of enquiry to follow. To paraphrase the words of the mathematician Johannes Kepler, perhaps designers of stethoscopes might simply have been thinking God’s thoughts (about the design of cats’ ears) after Him.5
Competing interests
No relevant disclosures.
References
- Martin LG. What is the function of the human appendix? Sci Am 1999; Oct 21: 14. 0_i1115608
- ARKive. Red fox fact file. http://www.arkive.org/red-fox/vulpes-vulpes/image-A7165.html (accessed Nov 2012).
- Strain GM. Deafness in dogs and cats. Hearing frequency ranges for dogs and other species. http://www.lsu.edu/deafness/deaf.htm (accessed Nov 2012).
- Peck A. Now I hear. The history of the stethoscope. Charleston, Ill: Antique Scientifica, 2011: 47-52. 0_i1115614
- Coppedge DF. The world’s greatest creation scientists from Y1K to Y2K. http://creationsafaris.com/wgcs.htm (accessed Nov 2012).