Kalischer coined the term "musculus sphincter urogenitalis" for the skeletal urethral sphincter and introduced the concept of the trigonal sphincter (the extension of the deep trigone).
Embryologically, the trigone of the bladder is derived from the caudal end of mesonephric ducts, which is of mesodermal origin (the rest of the bladder is endodermal).
In the open medulla, it is visible as what is known as the "hypoglossal trigone", a raised area (medial to the vagal trigone) protruding slightly into the fourth ventricle.
It is a very common finding in bladder biopsies and cystectomies, and most often found in the trigone area.
This plexus appears near the cribriform plate and travels posteriorly toward the olfactory trigone, medial olfactory gyrus, and lamina terminalis.
