label: urogenital sinus
label_lc: urogenital sinus
description: "The urogenital sinus (UGS) (TS:18-TS:28) is the epithelial lined cavity seen extending from the anterior cloaca. The epithelium is derived from cloacal endoderm. At TS:19, the paired nephric ducts are attached to its dorsolateral sides. Comprised of epithelium of urogenital sinus epithelium lining the lumen and the surrounding mesenchyme of urogenital sinus. The UGS is subdivided into the primitive bladder (cranial/anterior), the primitive bladder-caudal urogenital sinus transition zone, and caudal urogenital sinus (caudal/posterior), at the connection site of the common nephric ducts (which connect the nephric ducts to the UGS at the urogenital sinus ridge). From TS:20 the UGS also includes developing vasculature of urogenital sinus and nerves of urogenital sinus. The primitive bladder will develop into the bladder and the caudal urogenital sinus into the pelvic urethra. From TS:19-21 is comprised of three major regions; primitive bladder, primitive bladder-caudal urogenital sinus transition zone and caudal urogenital sinus. From TS:22-TS:28 it is comprised of three major regions; pelvic urethra, bladder-urethra transition zone and bladder."