Final answer:
In flexible diaphragms, the diaphragm muscle deforms, altering the volume of the thoracic cavity to enable breathing. It is a domed-shaped muscle that contracts and relaxes, influenced by thoracic wall compliance.
Step-by-step explanation:
In regards to a flexible diaphragm, it's the diaphragm muscle itself that deforms during breathing. The diaphragm is a large, domed-shaped skeletal muscle located under the lungs, separating the thoracic cavity from the abdominal cavity. When breathing, the diaphragm alternately contracts and relaxes, altering the volume of the thoracic cavity to facilitate inspiration and expiration. The concept of thoracic wall compliance also plays a role in this context, which is the ability of the thoracic wall to stretch under pressure, directly influencing the capacity of the lungs to expand during breathing.