The [prostatic sinuses] (sinus prostaticus) are bilateral depressions found lateral to the inferior portion of the median urethral crest (also known as the verumontanum). There are two prostatic sinuses within the prostatic urethra in the male

On the floor of these sinuses there are several perforations, representing the exit of the prostatic ducts (or ductules). These ducts bring prostatic fluid from the lateral lobes of the prostate into the urethra.

The image also shows the [prostatic utricle], also known as "utriculus prostaticus" or "utriculus", a small 6mm small dead-end channel found in the male prostatic urethra.

The word [utriculus] is Latin and means "little sac" or "little uterus".

Sources:
1. "The prostatic utricle is not a M?llerian duct remnant: immunohistochemical evidence for a distinct urogenital sinus origin" Shapiro E, Huang H, McFadden DE, et al. (2004) J Urol 172; 1753–1756
2. "Gray's Anatomy"38th British Ed. Churchill Livingstone 1995
3. "Tratado de Anatomia Humana" Testut et Latarjet 8 Ed. 1931 Salvat Editores, Spain

    Anterior view of a section of the prostate gland. The blue dotted line shows the edges of the prostatic urethra.