Step 1: Look just behind the internal urethral opening on the bladder floor and you find a small bump in the mucosa known as the uvula vesicae.
Step 2: The structure pushing the mucosa up at that midline spot is the median lobe of the prostate, which sits between the urethra and the ejaculatory ducts.
Step 3: This same median lobe is the typical culprit in benign prostatic enlargement, where its growth can indent and obstruct the bladder neck.
Step 4: The anterior, posterior, and lateral lobes are positioned away from this midline elevation, so they cannot account for the uvula vesicae.
\[\boxed{\text{Median lobe}}\]