The muscles occupying the anterior perinæal space require to be removed, Fig. 1, Plate 53, in order to expose the urethra, B M, the crus penis, D, and the deep perinæal fascia. The fascia will be now seen stretched across the subpubic triangular space, reaching from one ischio-pubic ramus to the other, whilst by its lower border, corresponding with the line of the transversae perinaei muscles, it becomes continuous with the superficial fascia, in the manner before described. The deep perinæal fascia (triangular ligament) encloses between its two layers, C E, on either side of the urethra, the pudic artery, the artery of the bulb, Cowper’s glands, and some muscular fibres occasionally to be met with, to which the name “Compressor urethrae” has been assigned. At this stage of the dissection, as the principal vessels and parts composed of erectile tissue are now in view, their relative situations should be well noticed, so as to avoid wounding them in the several cutting operations required to be performed in their vicinity.
Along the median line (marked by the raphe) from the scrotum to the coccyx, and close to this line on either side, the vessels are unimportant as to size. The urethra lies along the middle line in the anterior perinæal space; the rectum occupies the middle in the posterior space. When either of these parts specially requires to be incised—the urethra for impassable stricture, &c., and the lower part of the rectum for fistula in ano—the operation may be performed without fear of inducing dangerous arterial haemorrhage. With the object of preserving from injury these important parts, deep incisions at, or approaching to, the middle line must be avoided. The outer (ischio-pubic) boundary of the perinaeum is the line along which the pudic artery passes. The anterior half of this boundary supports also the crus penis; hence, therefore, in order to avoid these, all deep incisions should be made parallel to, but removed to a proper distance from this situation. The structures placed at the middle line, B M F, Fig. 2, Plate 52, and those in connexion with the left perinæal boundary, D G L, require (in order to insure the safety of these parts) that the line of incision necessary to gain access to the neck of the bladder in lithotomy should be made through the left side of the perinaeum from a point midway between M, the bulb, and D, crus penis above, to a point, K, midway between the anus, F, and tuber ischii, G, below. As the upper end of this incision is commenced over the situation of the superficial perinæal artery and the artery of the bulb, the knife at this place should only divide the skin and superficial fascia. The lower end, K, just clears the outer side of the dilated lower part of the rectum. The middle of the incision is over the left lobe of the prostate gland and neck of the bladder, which parts, together with the membranous portion of the urethra, are still concealed by the deep perinæal fascia, the structures between its layers, and the anterior fibres of K, the levator ani muscle. The incision, if made in due reference to the relative situation of the parts above noticed, will leave them untouched; but when the pudic artery, or some one of its branches, deviates from its ordinary course and crosses the line of incision, a serious haemorrhage will ensue, despite the anatomical knowledge of the most experienced operator. When it is requisite to divide the superficial and deep sphincter ani as in the operation for complete fistula in ano, if the incision be made transversely in the ischio-rectal fossa, the haemorrhoidal arteries and nerves converging towards the anus will be the more likely to escape being wounded.
DESCRIPTION OF THE FIGURES OF PLATES 50 & 51.
PLATE 50.
FIGURE 1.
A. The umbilicus.
B. The linea alba.
C. The suspensory ligament of the penis.
D D. The two corpora cavernosa penis.
E E**. The hypogastric and scrotal superficial fascia.