DISEASES OF THE MALE URETHRA.
It is hardly necessary in a work of this kind to enter into an elaborate description of the anatomy and physiology of the male urethra. There are a few points, however, which are of practical interest in the clinical and pathological study of its diseases. The urethra may be described as a musculo-membranous tube extending from the meatus urinarius to the bladder. It is divided into three portions, the penile, spongy, or pendulous urethra, the membranous, and the prostatic. The two latter comprise the fixed or deep urethra. The spongy or penile urethra is about six inches in length and extends from the meatus urinarius to the opening in the triangular ligament, at which point it joins the pars membranosa. The latter is about three-fourths of an inch in length and extends from the anterior to the posterior layer of the triangular ligament; the balance of the canal is comprised in the prostatic portion, which is about one and one-fourth inches long. The meatus urinarius is the nar rowest portion of the canal for the obvious purpose of better directing the outflowing semen and urine. The meatus varies con siderably in size. A small meatus is not necessarily an indica tion for a surgical operation, but when a small-calibred orifice is associated with urethral disease or possible reflex disturbance of the genitourinary tract, a congenital contraction of the meatus at once assumes surgical importance. The meatus is sometimes nar rowed because of the comparatively great thickness of that portion of the glans forming the floor of the fossa navicularis, the latter being the relatively dilated portion of the urethra, situated within the boundaries of the glans penis and terminating at the junction of the latter with the corpora cavernosa. In other cases the relative narrow ness of the meatus is due to a thin membranous fold at the inferior commissure of the orifice. This is dilatable and offers little or no re sistance to instrumentation, the contrary being true of the variety of narrowing previously mentioned. Narrowness of the meatus is usu ally congenital, destructive ulceration being the usual cause of ac quired contraction. In some instances the canal is relatively narrow
because of the presence of a congenital band just within the meatus, the orifice proper being fairly dilatable.
The spongy urethra is so-called because of its investment by the corpus spongiosum. The mucous membrane of this portion of the canal is abundantly supplied with mucous glands and ducts. These when infected are likely to become dilated and their orifices more or less obstructed with a resultant accumulation of infectious products in the glandular tissue proper. Latent infection and successive auto inoculations with gonorrhoea are often thereby explained. As is well known, these ducts and follicles may be so dilated that they catch the points of instruments employed in exploration of the urethra. They may also be the starting-point of urinary abscess and fistula. Their abundance and the difficulty of rendering them aseptic is a logical explanation of the obstinacy of some cases of urethritis.
The membranous portion of the canal is invested by relatively powerful layers of longitudinal and circular muscular fibres, the com pressor urethra and accelerator urines muscles. On this account it has been sometimes termed the muscular portion. The function of the muscular structures of the urethra is very important. That of the membranous urethra constitutes the true sphincter of the bladder. This muscular tissue is under the volitional control of the patient, but in rather a peculiar fashion. It would seem that the sympathetic nerve fibres supplied to the muscle are responsible for its normal tonicity. Voluntary nerve fibres supplied to the part enable the patient to in hibit the normal contraction at will, as a consequence of which the steady pressure or normal tonus of the detrusor urine muscle is en abled to overcome the slight remaining resistance of the true vesical sphincter, with resulting voluntary micturition. Direct or reflex ex citation of this portion of the canal is likely to result in retention of urine. Conversely, paralysis of the pars membranosa produces urinary incontinence.