The bladder is a muscular sac lined with a transitional cell epithelium and, in part, covered by the peritoneum. The bladder wall is mainly composed of a muscle, the detrusor. As it funnels down to its outlet, the bladder incorporates a second muscle, the sphincter. The sphincter occupies the area between the junction of the bladder and its drainage tube, the urethra. This is known as the bladder outlet. Up to this point, apart from its greater thickness of detrusor and sphincter muscle, the male bladder is similar to that of the female. Thereafter, the bladder outlet in the male becomes incorporated into the joint functions of the male urinary and genital tracts and, in particular, the dual use of the urethra in the regular voiding of urine and occasional ejaculation of seminal fluid.