How does a turtle breathe?

We humans (And just about all other land vertebrates) breathe by expanding our chest cavity, thus creating a partial vacuum in our lungs which are filled by air flowing through the nose and mouth via the trachea.

How does a turtle/tortise/terapin, with a fixed chest cavity
due to its shell, draw breath?

It doesn’t have a fixed chest cavity – the shell is in two parts, connected by hinges. Next time you have a chance to observe a turtle at close range, you’ll see the top half of the shell rise and fall with each breath.

It swallows air, according to my zoology textbook. I assume that this means it forces air into its lungs using its throat muscles.

-Ben

Not quite.

Most turtles’ carapaces (top shells) are indeed fused rigidly to their bottom shells (plastrons). If you watch a turtle breathing air, you’ll see the soft flesh exposed in the front and back of the shell softly pulsating in rhythm with its breathing.

Aquatic turtles absorb oxygen through the mucous membranes in their throats and anuses as well.

Although it is true that some turtles have hinged plastons, in general the shell prevents normal expansion and contraction of the body wall.

Instead they utilize specially paired muscles. One set each for expiration and inspiration. The first set compresses the viscera against the lungs to exhale. The second set acts a bit like a diaphragm by contracting and pulling the viscera back up against the body wall ( thereby expanding the body cavity, without expanding the body wall ) for inhalation.

In addition this can be supplemented by rotating the shoulder girdle and pelvic bones backwards and forwards to help pump air. However, this technique is likely of secondary importance.

  • Tamerlane