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3b. 5. The Female Urethra
(Urethra Muliebris)
The female urethra (Fig. 1139) is a narrow membranous canal, about 4 cm. long, extending from the internal to the external urethral orifice. It is placed behind the symphysis pubis, imbedded in the anterior wall of the vagina, and its direction is obliquely downward and forward; it is slightly curved with the concavity directed forward. Its diameter when undilated is about 6 mm. It perforates the fasciæ of the urogenital diaphragm, and its external orifice is situated directly in front of the vaginal opening and about 2.5 cm. behind the glans clitoridis. The lining membrane is thrown into longitudinal folds, one of which, placed along the floor of the canal, is termed the urethral crest. Many small urethral glands open into the urethra.Structure.—The urethra consists of three coats: muscular, erectile, and mucous. The muscular coat is continuous with that of the bladder; it extends the whole length of the tube, and consists of circular fibers. In addition to this, between the superior and inferior fasciæ of the urogenital diaphragm, the female urethra is surrounded by the Sphincter urethræ membranaceæ, as in the male. A thin layer of spongy erectile tissue, containing a plexus of large veins, intermixed with bundles of unstriped muscular fibers, lies immediately beneath the mucous coat. The mucous coat is pale; it is continuous externally with that of the vulva, and internally with that of the bladder. It is lined by stratified squamous epithelium, which becomes transitional near the bladder. Its external orifice is surrounded by a few mucous follicles.
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