Final answer:
The skeletal muscle mentioned in the text is the diaphragm, a critical respiratorially-active, domed-shaped muscle that divides the thoracic and abdominal cavities.
Step-by-step explanation:
The skeletal muscle described in the text is the diaphragm. This domed-shaped skeletal muscle is positioned below the lungs and operates as a critical component in breathing. It extends across the ribcage as a sheet at the base of the thorax, effectively separating the thoracic cavity from the abdominal cavity.
When the diaphragm contracts, it flattens, increasing the space in the thoracic cavity and facilitating the inflow of air into the lungs. Conversely, upon relaxation, the diaphragm resumes its dome shape, assisting in the expulsion of air from the lungs.
The diaphragm is a sheet of skeletal muscle that separates the thoracic cavity from the abdominal cavity and plays a crucial role in the process of breathing. Contraction and relaxation of the diaphragm contribute to changes in thoracic volume, allowing for inhalation and exhalation.