The female urethra, 1½ inches long, runs downwards and forwards in a slight curve, pierces the triangular ligament, between the layers of which it is surrounded by the compressor urethral, and ends at the external orifice 1 inch below and behind the clitoris and between the labia minora. The posterior wall is closely associated with the anterior vaginal wall, the peritoneum only dipping in between the postero-superior wall of the bladder itself and the body of the uterus. The canal normally is about 1/3 inch in diameter, but is very distensible, so that calculi may be passed or extracted per urethram in the female. Stones up to ¾ inch diameter may be so removed. A small vascular papillomatous tumour, which is painful, may occur about the orifice of the urethra, and is called a urethral caruncle.
The urethra in the male is fully 8 inches long, and in addition to the urine, transmits the spermatic fluid from the testicles, and the secretions from the prostate and Cowper's glands. Leaving the narrow orifice of the bladder, it passes through the prostate gland, and then, passing through the triangular ligament, enters the perineum, and penis. It is described as consisting of a prostatic, membrarrous, and spongy portions ; and in its course it describes a double curve, first passing down beneath, and then up in front of the pubic arch, and then once more turning down to enter the penile portion. The first curve with the convexity downwards is fixed, and begins and ends at the level of a horizontal line, drawn antero-posteriorly across the lower border of the symphysis, the summit lying 1 inch below the same point on the symphysis. The second curve commences at the point of attachment of the suspensory ligament, traverses the penis, and is movable.
The prostatic portion extending from the floor of the bladder to the prostate apex is the widest portion of the urethra (½ inch in diameter), is about 1¼ inches long, and is almost vertical. Wider at its centre than at either extremity, it begins opposite the centre of the symphysis posteriorly, and extends to a point 1 inch behind and below the subpubic angle. The verumontanum, continuous with the uvula vesica of the bladder, and distally with the crista urethralis, which disappears at the membranous portion, forms a ridge on its posterior border, and on its summit presents an opening, leading upwards and backwards for nearly ½ inch, called the prostatic utricle (or sinus pocularis), which is the homologue of the uterus and vagina of the female. The ejaculatory ducts open on either side of this utricle, while the larger prostatic ducts open into grooves, the prostatic sinuses, on either side of the verumontanum.
The membranous portion is the shortest, measuring about ¾ inch ; narrowest, except the meatus (½ inch in diameter) ; and is also the most fixed, lying between the two layers of the triangular ligament, and surrounded by the fibres of the compressor urethrce, which may produce what is called spasmodic stricture. It is separated from the subpubic ligament by the dorsal vessels and nerves of the penis, together with loose connective tissue.
The spongy portion is the longest, over 6 inches, and extends from the anterior layer of the triangular ligament to the meatus. Almost immediately after piercing the triangular ligament, the urethra enters the bulb ½ inch from its posterior extremity, and traverses its dorsal aspect, receiving the orifices of the ducts of Cowper's glands on its lower wall. The diameter of the spongy portion is considerable at the bulb, and thereafter is fairly uniform, save near the meatus. It presents numerous small lacunae and ducts of mucous glands, which open obliquely in the direction of the meatus, particularly on the floor of the canal. The fossa navicular is is a dilatation on the dorsal aspect, situated just beyond the meatus. A small recess, termed the lacuna magna, sometimes opens off it. The external meatus is the narrowest portion of the entire canal, measuring not more than ¼ inch in diameter. As the external meatus is the narrowest part of the urethra, a catheier which will pass that point will pass into the bladder if the canal be normal. The canal generally is only a potential one, and presents as a vertical slit at the meatus, and in the region of the fossa navicularis, and as a horizontal slit at other places.
In introducing a catheter, the penis is directed upwards, so as to obliterate the double curve, and, once the catheter has passed the fossa navicularis, its point is directed constantly toward the roof of the canal, as, if it be small, it might otherwise engage in the ducts opening on the floor. The point where difficulty is most likely to be experienced is at the junction of the wide movable penile and narrow fixed membranous portion, and here, if the point be allowed to pass along the floor, which is very dilatable at this point, it will probably not enter the narrow membranous canal, but rupture the urethra, making a false passage in the bulbous portion in front of the triangular ligament. To avoid this mistake, the handle of the instrument, which hitherto has been lying on the groin or abdomen of the patient, should now be steadily raised, so as to keep the point on the firmer roof, and usually it then slips in without any application of force.
Stricture from gonorrhoea generally affects the spongy portion, whereas stricture following trauma (as rupture from a fall stride-legs) generally affects the membranous portion. A primary syphilitic sore, occurring just within the urethral orifice, may cause stricture at that part. In cases of stricture, not merely is the canal narrowed, but it frequently is rendered tortuous, rendering catheterization very difficult, and greatly increasing the risk of making false passages. When the urethra is torn, whether by trauma, as in a fall stride-legs, by fractured pelvis, false passage, or ulcerative processes, extravasation of urine is liable to occur. Where the membranous portion is torn, the extravasation takes place between the layers of the triangular ligament, by which it is confined, until set free by sloughing, generally of the anterior layer, when it enters the perineum. Where the bulbous portion is affected, the urine is extravasatcd in the perineum between the anterior layer of the triangular ligament and the deep layer of the superficial fascia (Colles's fascia).
Colles's fascia is attached posteriorly to the base of the triangular ligament, and laterally to the rami of the pubes and ischium, and thus the urine, as it accumulates, is forced to run forwards. Colles's fascia is continuous with the dartos of the scrotum, and superficial fascia of the penis, while, by a funnel-shaped process running in front of the cord, it communicates with the superficial fascia of the abdomen. Thus the extiavasated urine first distends the perineum, then the scrotum and penis, and then finds its way on to the front of the abdomen, whence it is prevented reaching the thigh by the attachment of the fascia to Poupart's ligament. The urethral mucous membrane is supplied by the pudic nerve.