The muscle fibers arise on either side from the margin of the inferior ramus of the pubis.

[7][10] Voiding urine begins with voluntary relaxation of the external urethral sphincter.

This is facilitated by inhibition of the somatic neurons in Onuf's nucleus via signals arising in the pontine micturition center and traveling through the descending reticulospinal tracts.

This article incorporates text in the public domain from page 431 of the 20th edition of Gray's Anatomy (1918)

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