**Core Concept**
The trigone of the bladder is a smooth, triangular area of the bladder's internal surface, bounded by the two ureteric orifices and the internal urethral orifice. It plays a crucial role in the storage and micturition of urine.

**Why the Correct Answer is Right**
The trigone of the bladder is a muscular area composed of the detrusor muscle. It is innervated by the pelvic splanchnic nerves and is responsible for the closure of the ureteric orifices during micturition, preventing retrograde flow of urine into the kidneys. The trigone is also responsible for the maintenance of the antireflux mechanism, which prevents the backflow of urine from the bladder into the ureters.

**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect because the trigone is not responsible for the initiation of micturition, but rather for the maintenance of the antireflux mechanism during voiding.
**Option B:** This statement is incorrect because the trigone is not solely composed of smooth muscle; it is a muscular area composed of the detrusor muscle.
**Option C:** This statement is incorrect because the trigone is not responsible for the regulation of urine storage; it is involved in the micturition process.

**Clinical Pearl / High-Yield Fact**
The trigone of the bladder is a key area that is susceptible to injury during surgical procedures, such as transurethral resection of the prostate (TURP). Damage to the trigone can lead to urinary incontinence and other complications.

**Correct Answer: B. The trigone is not solely composed of smooth muscle.**