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Knowing what organ a dog doesn't have is helpful considering that we can be certain our dogs will never develop health issues associated with such organ. 

Indeed, this little organ spares dogs from the major hassle of dealing with a potentially life threatening complication that often ends humans under the surgical knife for an emergency operation. Can you guess what organ this is?

The Science of Comparative Anatomy

Comparative anatomy is the term used to depict the scientific study of the many body structure differences between animals of different species.

It all started when in 1555, French naturalist Pierre Belon, compared the bones of humans and birds and discovered how they shared several similar elements.

After several years, more and more experts started comparing the anatomy of various different animals.

All of this research has benefited in many ways, providing a more profound understanding of the impact the environment has on the development of certain body parts and any possible connections among species due to sharing a common ancestor.

What Organ Does A Dog Not Have?

Among several differences between the anatomy of dogs and humans, one specific organ has been noticed to be missing in dogs, can you guess what organ this is?

The missing organ is the appendix, a tube-shaped structure found by the colon in the lower right quadrant of the abdomen.

When the appendix in humans gets red and angry, it causes severe abdominal pain accompanied by fever, nausea and vomiting.

While dogs may also develop these symptoms, they are rather associated with something else rather than the appendix, for the simple fact that dogs don't have an appendix!

So while a dog's body shares many similar body features with us humans, the appendix is definitively not one of them!

A dog's perfect excuse.....

A dog's perfect excuse.....

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Not Useless as Thought

In humans, the appendix has been considered pretty much useless for many years, so much so, that people can live without one without encountering any problems.

However, recent research conducted at Duke University Medical School, has found that the appendix instead has likely a function, and a very important one too!

The study's findings suggest that the appendix works as a reservoir for good bacteria.

Surgery professor Bill Parker, co-author for this study, claims that this reservoir is possibly there for a specific purpose: to help recover in the case of a sudden depletion of good bacteria as it can happen with serious diseases such as cholera or amoebic dysentery.

Despite its usefulness, professor Parker though claims that the appendix should be still taken out when inflamed as appendicitis can turn deadly!

Dogs don't have an appendix, but they have the cecum

Dogs don't have an appendix, but they have the cecum

An Alternate Structure

Even though several animals along with the dog don't have an appendix, they seem to depend on some alternate structures.

Even though they might not be as effective as the appendix, they're still capable of storing good bacteria, explains professor Parker, this time in an article for Duke Magazine.

In particular, the cecum, a pouch-like structure, located at the junction of the small and large intestine, may work as a reservoir for beneficial bacteria in the eventuality of severe diarrhea. Just like the appendix does in humans, explains veterinarian James C. Coghlan, in the book: "Paleopet: The real reason your dog or cat eats grass."


  • Paleopet: The real reason your dog or cat eats grassKindle Edition, by James C. Coghlan DVM Booktango (December 18, 2012)
  • NBC News, Scientists May Have Found Appendix's Purpose, retrieved from the web on June 28th, 2016
  • Duke Magazine, Volume 94, No.2, March-April 2008, An Evolutionary Curiosity, retrieved from the web on June 28th, 2016

Photo credits:

  • Cieco (parte dell'intestino crasso) by Adert - Own work. CC BY-SA 3.0, modified to add captions.

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