Reptiles are tetrapods and breathe through lungs. The thoracic cavity has the diaphragm which is analogous to the mammalian diaphragm. Some of the reptiles like tegu lizards, have proto diaphragm, which separates the pulmonary cavity from the visceral cavity but do not help in inflation of lungs. The muscles for the crocodilian diaphragm pull the pubis and pulls the liver downwards which helps in expansion of lungs.