It also supplies one or two branches to the bulb and the corpus spongiosum penis. The dorsal nerve of the penis follows the pudic artery between the two layers of the triangular ligament, where it lies more completely under shelter of the side of the pubic arch than the artery. Finally, piercing the superficial layer of the triangular ligament, about half an inch below the symphysis pubis, it accompanies the dorsal artery of the penis. At the root of the penis it supplies one or two twigs to the corpus cavernosum. The dissection of the perineum is now completed, but whilst the body is in the lithotomy position, and the various parts of the perineum exposed, the student should consider what structures still cover the perineal aspect of the prostate gland. Three layers would still require to be removed to bring the prostate into view-viz. (1) the compressor urethræ muscle; (2) the parietal pelvic fascia or the deep layer of the triangular ligament; (3) the anterior fibres of the levator ani muscle. Such being the case, it will be apparent that within the limits of the urogenital triangle, and dissecting from the surface towards the prostate gland, we meet with an alternation of muscular and fascial strata, viz. : 1. The fascia of Colles. 2. Superficial perineal muscles. 3. Triangular ligament. 4. Compressor urethra muscle. 5. Parietal pelvic fascia or deep layer of triangular ligament. 6. Levator ani muscle. 7. Capsule of prostate. Further, the fascia of the urogenital triangle are so arranged that they form a superficial and a deep compartment, and within one or other of these all the structures of this division of the perineum are contained (Fig. 78). The superficial compartment is bounded in front by the fascia of Colles, behind by the triangular ligament, laterally by the attachment of these to the margins of the pubic arch, and inferiorly by the blending of the fascia of Colles with the base of the triangular ligament. For the contents of this compartment see p. 340 (Fig. 78). The deep compartment is the interval between the triangular ligament and the parietal pelvic fascia, and the structures which it contains are enumerated at p. 357 (Fig. 78). Surgical Anatomy of Perineum.-In the rectal triangle the fatty tissue which fills up the ischio-rectal fossa is very liable, under certain circumstances, to inflammation. When pus forms, a knowledge of the FIG. 79.-Deep dissection, in which the lower portion of the levatores ani muscles have been removed, and the external sphincter detached from the central point of the perineum, and the rectum turned back.-(From GRAY'S Anatomy.) structures which compose the walls of the fossa will show why fistula in ano so frequently results. The pus cannot pass upwards into the pelvis on account of the union of the visceral and parietal parts of the pelvic fascia; its passage outwards is resisted by the strong parietal layer of the pelvic fascia; whilst inferiorly the dense integuments of The inner wall Here the gut is the hip prevent it from pointing towards the surface. of the space, however, offers a weak resistance. guarded, it is true, by the rectal layer of the pelvic fascia, but in the lower part of the rectum this is very thin, and soon gives way before the continued pressure of the pus. The wall of the rectum then becomes thinned, and ultimately perforated, and the pus is voided through the anal orifice, giving rise to fistula. The lesson to learn from this is, that in every case of inflammation of the ischio-rectal fat an early incision should be made into the fossa so as to give free vent to the pus, and thus prevent its burrowing through the wall of the rectum. In the lateral operation of lithotomy an accurate knowledge of the anatomy of the perineum is of great importance to the surgeon. He should know not only the structures which require to be divided, but also those which he must avoid, and how to avoid them. In the first incision, which begins in the middle line an inch and a half in front of the anus, and extends backwards and outwards into the left ischiorectal fossa midway between the anus and ischial tuberosity, the following parts are cut :-(1) skin and superficial fascia; (2) transversus perinei muscle and the transverse perineal artery; (3) the lower or posterior edge of the triangular ligament; (4) the inferior hæmorrhoidal vessels. The forefinger of the left hand is introduced into the middle of the wound and pushed upwards behind the triangular ligament until the groove of the staff, as it lies in the membranous part of the urethra, is felt. The point of the knife is now placed in the groove, and the blade lateralised. The knife is then carried steadily along the groove into the bladder. In this incision the structures divided are- (1) the membranous and prostatic portions of the urethra; (2) the deep layer of the triangular ligament; (3) the compressor urethræ muscle; (4) the anterior fibres of the levator ani muscle and the left lateral lobe of the prostate. The dangers of this operation may be considered to be three in number (1) the artery to the bulb; (2) the pudic artery; (3) the rectum. Division of the artery to the bulb is an exceedingly awkward accident. The hæmorrhage resulting is very profuse, and exceedingly difficult to check on account of the short course of the vessel, its depth, and also its close connection with the layers of the triangular ligament which prevent it from retracting freely when cut. When this artery is in its normal position-i.e., from a quarter to half an inch above the base of the triangular ligament-there should be little difficulty in avoiding it. In the first part of the operation it is merely the lower or posterior edge of the triangular ligament which is cut. Again, when the finger is introduced, so as to feel the staff in the membranous part of the urethra, the artery should lie in front of and superficial to it. When the artery to the bulb arises further back, as it sometimes does, it will, in all probability, be cut; and there is no way of avoiding this, seeing that there are no means by which we can discover this abnormal origin beforehand. The pudic artery runs no danger until it has given off the artery to the bulb, and has left the shelter of the pubic arch to lie between the layers of the triangular ligament. The risk of wounding this vessel is very slight, and it could only occur in the careless withdrawal of the knife. The superficial perineal branch of the pudic is frequently cut in the early stages of the operation, but under ordinary circumstances there is little difficulty in securing it. It has been stated, however, that if it should happen to be divided close to its origin, it might retract within Alcock's canal. The accident might then be very nearly as awkward an occurrence as a wound of the main vessel itself. Although the rectum lies in close proximity to the membranous and prostatic parts of the urethra, it is very rarely injured. It is the invariable practice of the surgeon to empty the rectum by an enema prior to the operation. A pad of tow, soaked in a mixture of spirit and carbolic acid, should be placed in the perineum, and the flaps of skin carefully stitched over it. On the third day, after the body has been brought into the Rooms, it is placed upon its face, and the dissectors of the abdomen stop work until the subject is turned, which is done four days later. THE FEMALE PERINEUM. The boundaries of the female perineum are identical with those in the male. The region, however, is wider and of greater extent. For purposes of description, it is subdivided by an imaginary transverse line drawn in front of the anus and the tuberosities of the ischium into a posterior rectal triangle and an anterior urogenital triangle. External Anatomy.-The rectal triangle presents the same points for consideration as in the male. The external anatomy of the urogenital triangle demands the careful study of the student, because here we find the external organs of generation. I. The mons Veneris. 2. The labia majora. 3. The labia minora. They are 4. The clitoris. 5. The urethral opening. All these parts are included under the common term of Vulva. The Mons Veneris is a marked cushion-like eminence situated in front of the pubes. This projection is due to a collection of adipose tissue under the integument. It is covered with short crispy hair. The Labia Majora correspond to the scrotum in the male, cleft along the middle line. They are two rounded folds, which commence in front at the mons Veneris and FIG. 80.-Outlet of pelvis. extend downwards and backwards towards the anus. They diminish in thickness as they proceed backwards, and anteriorly they unite to constitute the anterior commissure. Externally, they are covered by skin studded with scattered hairs, whilst internally they are coated with smooth humid integument, the free surface of which is lubricated by an unctuous semi-solid secretion, derived from numerous sebaceous glands which open upon it. During parturition, the labia majora are unfolded, and thus give the vagina a greater capability of dilatation. The labia majora enclose an elliptical fissure, which is termed the pudendal cleft, or the urogenital fissure, on |