The respiratory system of the turtle is modified to accomodate some peculiar morphological features. Notice the trachea, which has become elongated in response to the posterior migration of the heart and viscera and, in part, to the extendable neck (Lawson 1979). Also notice the spongy texture of the lungs created by the network of air passages, called faveoli (Kardong 1998).
The shell of the turtle poses a special problem in the ventilation of the lungs. The rigidity of the shell prevents the use of the ribs in the aspiration pump. Alternatively, turtles possess sheets of muscle within the shell that, through contraction and relaxation, force air in and out of the lungs. In addition, turtles can alter the pressure within the lungs by moving the limbs in and out of the shell (Kardong 1998).