The most important characteristic of the tortoise skeleton is that a large part of its spine is welded to the dorsal part of the carapace. The skeleton makes breathing impossible by movement of the rib cage; It is carried out mainly by the contraction of the modified abdominal muscles that function analogously to the diaphragm of the mammals and by pumping movements of the pharynx

REFERENCE: Young, J. Z. 1977. La vida de los vertebrados. Editorial Omega, Barcelona, 660 pp. ISBN 84-282-0206-0