Changes

Some people now think that rather than an internal sphincter which contracts to resist urine outflow there is an actual structure which is opened when its muscle bundles contract.  This would mean in these species that urinary continence relies on the external sphincter.  It is not certain as yet which structure is correct but this idea does concur with the recent demonstration that the proximal urethra plays a role in urine storage in the dog and goat.

Some people now think that rather than an internal sphincter which contracts to resist urine outflow there is an actual structure which is opened when its muscle bundles contract.  This would mean in these species that urinary continence relies on the external sphincter.  It is not certain as yet which structure is correct but this idea does concur with the recent demonstration that the proximal urethra plays a role in urine storage in the dog and goat.