**Core Concept**
The trigone of the bladder is a triangular region formed by the two ureteric orifices and the internal urethral orifice. It plays a crucial role in the development and function of the bladder. The trigone is a muscular region composed of smooth muscle fibers.

**Why the Correct Answer is Right**
The trigone of the bladder is a unique region that is derived from the mesoderm of the cloaca, which is a common embryonic structure that gives rise to the bladder, urethra, and external genitalia. The trigone is also characterized by the presence of smooth muscle fibers that are continuous with the detrusor muscle of the bladder. This unique structure allows for coordinated contraction and relaxation of the bladder muscles during micturition.

**Why Each Wrong Option is Incorrect**
**Option A:** The trigone of the bladder is not derived from the mesoderm of the cloaca, which is a false statement.
**Option B:** The trigone is not composed of skeletal muscle fibers, which is incorrect.
**Option C:** The trigone is not a region of the bladder that is sensitive to stretch, which is not true.

**Clinical Pearl / High-Yield Fact**
The trigone of the bladder is a key region to identify during cystoscopy, as it is a landmark for the ureteric orifices and the internal urethral orifice.

**Correct Answer: B. The trigone is composed of smooth muscle fibers.**