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114 Commentary on plates 50 & 51.

The superficial fascia having invested the testicles each in a distinct sac, the adjacent sides of both these sacs, by joining together, form the median septum scroti, E, Fig. 2, Plate 50. In the perinaeum, Fig. 1, Plate 51, the fascia, A, may be traced from the back of the scrotum to the anus. In this region the mem­brane is found to adhere laterally to the rami of the ischium and pubes; whilst along the median perinaeal line the two sacs of which the membrane is composed unite, as in the scrotum, and form an imperfect septum. In front of the anus, beneath the sphincter ani, the fascia degenerates into cellular membrane, one layer of which is spread over the adipose tissue in the ischio-rectal space, whilst its deeper and stronger layer unites with the deep perinaeal fascia, and by this con­nexion separates the urethral from the anal spaces. The superficial fascia of the hypogastrium, the scro­tum, and the perinaeum forming a continuous mem­brane, and being adherent to the several parts above­ noticed, may be regarded as a general double sac, which isolates the inguino-perinaeal region from the femoral and anal regions, and hence it happens that when the urethra becomes ruptured, the urine which is extravasated in the perinaeum, is allowed to pass over the scrotum and the abdomen, involving these parts in consequent inflammation, whilst the thighs and anal space are exempt. The tunicae vaginales, which form the immediate coverings of the testicles, cannot be entered by the urine, as they are distinct sacs originally protruded from the abdomen. It is in consequence of the imperfect state of the inguino-peri­naeal septum of the fascia, that urine effused into one of the sacs is allowed to enter the other.

Like all the other structures which join on either side of the median line, the penis appears as a sym­metrical organ, D D, Fig. 2, Plate 50. While viewed in section, its two corpora cavernosa are seen to unite anteriorly, and by this union to form a septum "pectiniforme;" posteriorly they remain distinct and lateral, F F, Fig. 2, Plate 51, being attached to the ischio-pubic rami as the crura penis. The urethra, B, Fig. 2, Plate 50, is also composed of two sides, united along the median line, but forming between them a canal by the cleavage and partition of the urethral septum. All the other structures of the perinaeum will be seen to be either double and lateral, or single and median, according as they stand apart from, or approach, or occupy the central line.

The perinaeum, Figs. 1, 2, Plate 51, is that space which is bounded above by the arch of the pubes, be­hind by C, the os coccygis, and the lower borders of, I I, the glutaei muscles and sacro-sciatic ligaments, and laterally by D D, the ischiatic tuberosities. The osseous boundaries can be felt through the integuments. Be­tween the back of the scrotum and the anus the peri­naeum swells on both sides of the raphe, A B, Fig. 3, Plate 50, and assumes a form corresponding with the bag of the superficial fascia which encloses the struc­tures connected with the urethra. The anus is cen­trally situated in the depression formed between D D, the ischiatic tuberosities, and the double folds of the nates.

The perinaeum, Fig. 3, Plate 50, is, for surgical pur­poses, described as divisible into two spaces (anterior and posterior) by a transverse line drawn from one tuber ischii, D, to the other, D, and crossing in front of the anus. The anterior space, A D D, contains the urethra; the posterior space, D D C, contains the rec­tum. The central raphe, A B C, traverses both these spaces. The anterior or urethral space is (while viewed in reference to its osseous boundaries) trian­gular in shape, the apex being formed by the pubic symphysis beneath A, whilst two lines drawn from A to D D, would coincide with the ischio-pubic rami which form its sides. The raphe in the anterior space indi­cates the central position of the urethra, as may be ascertained by passing a sound into the bladder, when the shaft of the instrument will be felt prominently between the points A B. Behind the point B, the sound or staff sinks deeper in the perinaeum as it follows the curve of the urethra towards the bladder, and becomes overlaid by the bulb, &c.

The ischiatic tuberosities, D D, Fig. 3, Plate 50, are, in all subjects, sufficiently prominent to be felt through the integuments, &c.; and the line which, when drawn from one to the other, serves to divide the two perinaeal spaces, forms the base of the anterior one.

COMMENTARY ON PLATES 50 & 51. 115

In well-formed subjects, the anterior space is equiangular, the base being equal to each side; but according as the tuberosities approach the median line, the base becomes narrowed, and the triangle is thereby rendered acute. These circumstances influence the direction in which the first incision in the lateral operation of lithotomy should be made. When the tuberosity of the left ischium stands well apart from the perinaeal centre, the line of incision, B E, Fig. 3, Plate 50, is carried obliquely from above downwards and outwards; but in cases where the tuberosity approaches the cen­tre, the incision must necessarily be made more vertical. The posterior perinaeal space may be described on the surface by two lines drawn from D D, the ischiatic tuberosities, to C, the point of the coccyx, whilst the transverse line between D and D bounds it above.

By removing the integument and superficial fascia, we expose the superficial vessels and nerves, together with the muscles in the neighbourhood of the urethra and the anus. The accelerator urinae, E, Fig. 2, Plate 51, which embraces the urethra, and the sphincter ani, B C, which surrounds the anus, H, occupy the me­dian line, and are divided each into halves by a central tendon, E B C, which traverses the perinaeum from be­fore backwards, to the point of the coccyx. On either side of the anus, in the ischio-rectal space, D D, Fig. 1, Plate 51, is found a considerable quantity of granular adipose tissue, traversed by the inferior haemorrhoidal arteries and nerves-branches of the pudic artery and nerve.

In front of the anus are seen two small muscles (transversae perinaei), G G, Fig. 2, Plate 51, each arising from the tuber ischii of its own side, and the two be­coming inserted into, B, the central tendon. These transverse muscles serve to mark the boundary be­tween the anterior and posterior perinaeal spaces. Be­hind each muscle is found a small artery, crossing to the median line. The left transverse muscle and ar­tery are always divided in the lateral operation of lithotomy. On the outer sides of the anterior perinaeal space are seen the erectores penis muscles, F F, over­laying the crura penis. Between each muscle and the accelerator urinae, the superficialis perinaei artery and nerve course forwards to the scrotum, &c.

The perinaeal muscles having been brought fully into view, Plate 52, Fig. 1, their symmetrical arrange­ment on both sides of the median line at once strikes the attention. On either side of the anterior space appears a small angular interval, L, formed between B, the accelerator urinae, D, the erector penis, and E, the transverse muscle. Along the surface of this interval, the superficial perinaeal artery and nerve are seen to pass forwards; and deep in it, beneath these, may also be observed, L, the artery of the bulb, arising from the pudic, and crossing inwards, under cover of the ante­rior layer of the membrane named the deep perinaeal fascia. The first incision in the lateral operation of lithotomy is commenced over the inferior inner angle of this interval.

The muscles occupying the anterior perinaeal space require to be removed, Fig. 1, Plate 53, in order to expose the urethra, B M, the crus penis, D, and the deep perinaeal 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 perinaeal 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 perinaeal 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.