In connexion with the perineum, so much of the spongy portion of the urethm only as is covered by the acceleratores urinm muscles re quires to be considered, and of this the bulb constitutes the largest and most important part. The bulb is an oval swelling, in which the corpus spongiosum urethrw commences poste riorly, it varies in size according to the sub ject, being small during childhood, enlarging very much at puberty, and often presenting excessive dimensions in old men ; during erec tion, too, it is turgid and swollen, though at other times it remains comparatively flaccid. The length of the bulb, when well developed, may be estimated at an inch and a half, and its thickness or depth from the cavity of the urethra at about eight lines. Its posterior extremity is thick and overlaps the membranous portion of the ure thra, whilst anteriorly the bulb becomes gra dually narrower, but there is no exact line of demarcation between that body and the re mainder of the corpus spongiosum. The bulb is situated between the crura penis and in front of the triangular ligament of the urethra, to which it is connected by the expansion of fibrous membrane already described ; it is co vered by the acceleratores urin, and derives from them a muscular sheath all but perfect. The bulk of this body is constituted by a spongy erectile tissue, remarkably soft, and possessing intrinsically little powers of resist ance, but a thin fibrous membrane of invest ment affords it some protection from without. The canal of the urethra in this situation pre sents a slight dilatation (most observable infe riorly) named the sinus of the bulb, and the delicate ducts of Cowper's glands, two in num ber, open into the lower and lateral parts of the passage still further forwards. It should be particularly noted that the bulb, measured at the exterior, is in point of size quite out of proportion to the width of the corresponding part of the urethral canal, the canal presenting but a slight dilatation, whilst the dimensions of the bulb are very considerable; and of equal importance in practice is the fact that the axis of the bulb differs widely from the axis of the corresponding portion of the canal, the axis of the bulb running in a very oblique direction downwards and backwards towards the lower extremity of the rectum, whilst the axis of the canal lies upon a higher plane and runs much more nearly horizontally. backwards.
In a healthy urethra the principal difficulties of catheterism, whether performed by straight or by curved instruments, are encountered at this part of the passage : the sudden change in direction which the urethra here undergoes, the abrupt narrowing of the membranous por tion immediately behind the dilatation of the bulb, the mobility of the urethra in front of the triangular ligament, and its immobility where it passes through that structure, the ease with which a catheter perforates the delicate tissue of the bulb, and, above all, the striking difference in direction observable between the axis of the bulb and the axis of the correspond ing portion of the urethral canal, explain this sufficiently ; nor should it be forgotten that the muscular girth formed by the acceleratores urinm is often the seat of spasm.
The error in catheterism of most frequent occurrence here is the perforation of the floor of the urethra at the bulb, after which the ex tremity of the instrument passes between the rectum and the urethra. The surgeon commits this mistake by neglecting to depress the handle of the catheter in time to raise the point out of the sinus of the bulb into the mernbranous portion, and so much the more readily as the slightest force exercised in this wrong direction is sufficient to perforate the spongy tissue.
The premature depression of the handle of the catheter may likewise injure the urethra, but in a different manner, for if that ma noeuvre be executed too soon and with undue force, the point of the instrument will lacerate the upper wall of the canal anterior to the tri angular ligament.
A difficulty may, however, be experienced in entering the rnenibranous portion of the urethra, even though the handle of the catheter be depressed at the proper time; the surgeon in such cases fails to " hit off" the aperture in the triangular ligament which transmits the urethra, and the point of the instrument swerv ing laterally, comes to press against the front of the triangular ligament at one side of the orifice, instead of traversing the orifice itself. To guard against such a casualty, care must be taken to keep the point of the catheter fairly in the middle line, and (should any obstruction arise) to exercise slight traction upon the penis for the purpose of rendering tense the fibrous covering of the bulb, and in that manner stretching the opening in the triangular ligament.
From these principles it clearly follows that, except under peculiar circumstances, curved instruments are to be preferred, for their adapta tion to the curvature of the canal enables them to reach the bladder without exercising undue pressure upon any part of the passage ; whilst the straight staff conducted ever so skilfully must to a certain extent strain or disturb the permanently curved portion of the urethra. But, besides this obvious advantage, the natural impediments to catheterism (placed chiefly along the floor of the passage) are also most easily surmounted by the curved instrument, for its point can at any moment be readily raised by the operator whilst he accomplishes the same object muc'h more imperfectly in using the straight staff. It cannot be denied, however, that, for certain purposes, straight instruments possess a decided superiority, and therefore every surgeon should be prepared to employ them when the occasion suits.
The preceding outline describes with suffi cient accuracy the course and relations of the principal organs belonging to the perineum, and therefore it now only remains to study the anatomy of this region from below according. to the usual method of dissection. The subject is of course supposed to be placed in the ordinary position, with a full-sized staff introduced into the bladder, the rectum artificially distended, the scrotum raised and drawn forwards, the hands bound firmly to the ankles at each side respectively, the pelvis elevated on a block, and the knees sepamted to a convenient distance from each other.