The diaphragm is formed of all the following except
**Core Concept**
The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdominal cavity, playing a crucial role in breathing. It is primarily composed of skeletal muscle, but also contains other tissues such as tendons and aponeuroses.
**Why the Correct Answer is Right**
The diaphragm is formed of three main parts: the peripheral margin, the central tendon, and the muscular portion. The peripheral margin is a fibrous structure that attaches the diaphragm to the ribs and the lumbar vertebrae. The central tendon is a tough, fibrous plate that provides additional support to the diaphragm. The muscular portion is the main functional part of the diaphragm, responsible for contraction and relaxation during breathing. This portion is composed of three main muscle groups: the sternocostal, costal, and crural muscles.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, as the question only lists three options.
**Option B:** This option is not provided.
**Option C:** This option is not provided.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the diaphragm is a dome-shaped muscle that separates the chest cavity from the abdominal cavity, and its primary function is to facilitate breathing by contracting and relaxing during inspiration and expiration.
**Correct Answer:** Not provided, as the question only lists three options.