The urinary bladder has three coats—an outer incomplete peritoneal investment, a middle muscular coat, and an inner lining of mucous membrane.
The empty bladder is always collapsed, its walls being in apposition. A median sagittal section of the bladder and urethra shows a Y-shaped fissure lying between the symphysis pubis and the uterus, the uterus lying anteverted upon the upper surface of the bladder.
For convenience of description the bladder is divided into three parts—the corpus, or body, the fundus, or base; and the cervix, or neck.
The body of the bladder is all that portion that lies above the plane of the vesical orifices of the ureters and the center of the symphysis pubis.
The part lying below this plane is the base.
The vesical triangle, or the trigone, is that triangular area in the base of the bladder, the angles of which are marked by the vesical orifices of the ureters and the internal meatus of the urethra.
The neck of the bladder is the funnel-shaped portion where the bladder merges into the urethra.
The mucous membrane of the bladder is covered partly with squamous, partly with cylindrical epithelium. The mucous membrane is loosely attached to the muscular coat throughout the body of the bladder, so that when the organ is contracted the membrane is thrown into uneven folds. The mucous membrane is much more closely attached to the underlying structures in the region of the vesical triangle, and it here preserves a smooth surface when the bladder is collapsed.
The vesical triangle is more richly supplied with nerves than are the other portions of the bladder, and is consequently the most sensitive portion.
The vesical orifice of the ureter appears as a dimple, a small truncated cone, or a pin-hole or slit on the mucous membrane.