ACCELERATOR Urinae, a Muscle of the Penis, by some made a Pair of Muscles; thus called from its Office in expediting the Discharge of the Urine and Semen. See MUSCLE, PENIS, USE.

It arises tendinous from the upper and sore-part of the Urethra; but soon grows fleshy, passes under the Pubis, and encompasses the Bulb of the cavernous Body of the Urethra. Both sides of this Muscle meet in a middle line, corresponding to the Seam in the Skin over it; and continue so united, the space of two Inches; after which, it detaches two fleshy Elongations, which become thin Tendons at their Terminations on the cavernous Bodies of the Penis.

Its upper Part covering the Bulb, when in Action, straightens the Veins which pass through it from the Corpus Cavernosum of the Urethra; and hinders the Reflux of the Blood in an Erection; and by the repeated Contractions of this upper Part, drives the Blood in the Bulb towards the Glans. See ERECTION.

The two Elongations compress the Channel of the Urethra, and so force out the contained Seed, or Urine; whence the Muscle takes its Name. See URINE, and SEED.