The male genitourinary sphincter mechanism in the dog.

In an effort to locate and characerize a genital sphincter in the male posterior urethra, the intraluminal changes in urethral pressure under both sympathetic and parasympathetic stimulation were studied. It appears that the urethra has a specific genital sphincteric length corresponding to the supramontanal portion. The urethral length is seemingly under sympathetic control, so that backflow of semen does not occur during ejaculation. The urinary sphincter apparently involves the entire posterior urethra and is primarily under parasympathetic influence.