Membranous urethra

Narrowest part of the urethra

Membranous urethra
The male urethra laid open on its anterior (upper) surface. (Membranous part labeled at upper right.)
Dissection of the prostate showing the prostatic and membranous portions of the urethra (unlabeled)
Details
Identifiers
Latin	pars intermedia urethrae masculinae, pars membranacea urethrae masculinae
FMA	19674
Anatomical terminology [edit on Wikidata]

The membranous urethra or intermediate part of male urethra is the shortest, least dilatable, and, with the exception of the urinary meatus, the narrowest part of the urethra.

It extends downward and forward, with a slight anterior concavity, between the apex of the prostate and the bulb of the urethra, perforating the urogenital diaphragm about 2.5 cm below and behind the pubic symphysis.

The hinder part of the urethral bulb lies in apposition with the inferior fascia of the urogenital diaphragm, but its upper portion diverges somewhat from this fascia: the anterior wall of the membranous urethra is thus prolonged for a short distance in front of the urogenital diaphragm; it measures about 2 cm in length, while the posterior wall which is between the two fasciæ of the diaphragm is only 1.25 cm long. The anatomical variation in membranous urethral length measurements in men have been reported to range from 0.5 cm to 3.4 cm.

The membranous portion of the urethra is surrounded by the fibers of the sphincter urethrae membranaceae.

In front of it the deep dorsal vein of the penis enters the pelvis between the transverse ligament of the pelvis and the arcuate pubic ligament; on either side near its termination are the bulbourethral glands.

Additional images

Structure of the penis
Vertical section of bladder, penis, and urethra.

References

This article incorporates text in the public domain from page 1235 of the 20th edition of Gray's Anatomy (1918)

External links

Anatomy photo:43:08-0102 at the SUNY Downstate Medical Center - "The Female Pelvis: The Urethra"
Anatomy photo:44:06-0103 at the SUNY Downstate Medical Center - "The Male Pelvis: The Urethra"
MedEd at Loyola Grossanatomy/dissector/practical/pelvis/pelvis11.html

Male reproductive system

Internal

Seminal tract

Testicles	Layers Tunica vaginalis Tunica albuginea Tunica vasculosa Appendix Mediastinum Lobules Septa Leydig cells Sertoli cells Blood–testis barrier
Spermatogenesis	Spermatogonium Spermatocytogenesis Spermatocyte Spermatidogenesis Spermatid Spermiogenesis Spermatozoon
Other	Seminiferous tubules Tubuli seminiferi recti Retia testes Efferent ducts Epididymides Appendix Inferior ligaments Superior ligaments Stereocilia Paradidymides Spermatic cords Pampiniform plexus Vasa deferentia Ampullae Rectovesical pouch Ejaculatory ducts Testicular arteries Testicular veins

Accessory glands

External

Penis	Root Crura Bulb Fundiform ligament Suspensory ligament Body Corpora cavernosa Trabeculae of corpora cavernosa Corpus spongiosum Trabeculae of corpus spongiosum Glans Foreskin Frenulum Corona Septum glandis Fascia Superficial Deep Tunica albuginea Septum Raphe Arteries Arteries of bulb Dorsal arteries Deep arteries Internal pudendal artery Veins Dorsal veins Vein of bulb Internal pudendal veins Nerves Dorsal nerves Pudendal nerves Urethra Internal urethral sphincter Internal urethral orifice Pre-prostatic Prostatic Intermediate Spongy External sphincter muscle Navicular fossa Lacuna magna External urethral orifice Lacunae of Morgagni Urethral glands
Scrotum	Layers Skin Dartos fascia External spermatic fascia Cremaster Cremasteric fascia Internal spermatic fascia Ligament Raphe Septum Arteries Anterior scrotal arteries Posterior scrotal arteries Nerves Anterior scrotal nerves Posterior scrotal nerves Perineal nerve Posterior scrotal veins

Penis