Question

The structure that encloses the thoracic cavity of mammals at the bottom is made up of:

• A. Longitudinal muscle
• B. Circular muscle
• C. Elastic cartilage
• D. Radial muscle

Answer 1

The correct option is D Radial muscle

Diaphragm is a dome-shaped structure which encloses the thoracic cavity at the bottom. It is a muscular septum which divides the body cavity into upper thoracic cavity and lower abdominal cavity. It is made up of radial muscles which originate from the periphery and inserted in the central region of the diaphragm. By the contraction of these muscles, the diaphragm flattens and the volume of thoracic cavity increases which helps in inspiration. There is a central tendon in the central region of diaphragm which is pierced by 3 tubes namely oesophagus, aorta, and posterior vena cava.
Longitudinal and circular muscles are present in the muscular layer of stomach and oesophagus. Elastic cartilages provide strength and elasticity. It is present in epiglottis, cartilages of Santorini or larynx, outer ear pinna etc.