Bladder. The urinary bladder is a hollow receptacle in which the urine accumulates between the intervals of micturition. Into it open the ureters, and from it passes the urethra. The adult bladder is capable of holding about one pint; it lies in the pelvis, to the walls of which it is attached by various ligaments. Lining the interior of the bladder is a mucous membrane, and this is enveloped by a muscular coat, and finally the bladder is invested in part by peritoneum. The upper part of the bladder is called the apex, the portion adjoining the urethra is termed the neck, and the triangular area mapped out by the orifices of the two ureters and the urethra is called the trigone. Inflammation of the bladder is called cystitis. Tumours may develop, too, in connection with this viscus. For stone in the bladder, see Calculus.