The membranous portion of the urethm is situated within ten lines of the rectum, and the bulb projects still further backwards, lying but half an inch apart from that intestine, so that, in the lateral and also in the bilateral operations, the lithotomist incurs some risk of wounding the bowel as he lays bare the gr, oove in the staff. In the bilateral method the operator endeavours, by a semilunar incision carried across the recto•urethral triangular space, to reach the staff as it lies in the membranous portion of the urethm, and from the proximity of the bulb to the rectum both these parts are endangered as the knife traverses the interme diate space. In the lateral method the rectum is not so likely to be injured in the correspond ing step of the operation, because the bowel is further removed from the membranous portion of the urethra than from the bulb, and besides the urethm is incised somewhat upon its lateral aspect. In either case the surgeon best ensures the safety of the intestine by taking care to have the fwees evacuated before the opemtion com mences, by holding the staff well up into the arch of the pubis, and by directing the point of the knife forwards as he cuts into the urethm.
The recto-urethral tHangular space is the po sition usually occupied by that mre form of rupture, a perineal hernia ; in this disease the hernia leaves the abdominal cavity at the bottom of the great cul-de-sac of the peritoneum, and dmwing down the serous membmne in its pro gress it gradually insinuates itself between the prostate gland and the rectum, and at length protrudes between the rectum and the bulb. In the perineum the sac is in general rather su perficial. The tumor occasionally deviates from the middle line, and projects outwards and backwards behind the transversus perinei muscle into the ischio-rectal fossa; it rarely undergoes stmngulation, being in almost every instance reducible.
The prostate gland denaands the special at tention of the surgical anatomist, for much of the operator's success in lithotomy turns upon his knowledge of the relations, the size, and the density of' this organ as well as of the re sistance of its capsule. The prastate is heart shaped ; it has been also not unaptly compared to a chesnut. Its base, directed backwards and upwards, embraces the neck of the bladder, and usually presents a notch for the entmnce of the ejaculatory ducts; its apex, truncated and directed forwards and downwards, is in contact with Wilson's muscles and sepamted ffom the triangular ligament of the urethm by an interval of less than half an inch ; its under surface, grooved longitudinally in the middle line, looks somewhat backwards and rests u pon the rectum with the intervention of a quantity of rather dense cellular tissue, in which fat never accumulates; its upper surface, inclining slightly forwards and less extensive than the lower, is connected to the pubis by the anterior true ligaments of the bladder; and its sides, which are rounded, are covered by the levatores ani muscles. The vesicul seminales are re lated to the base of the prostate gland, and the dorsal veins of the penis lie upon its upper surface, which is scarcely three-quarters of an inch distant from the pubis. The rectum, when empty, is in contact with the under surface only of the prostate, but when distended, it also encroaches upon the sides of the gland ; this occurs to an extreme degree whenever the bowel presents the dilatation so commonly observed in elderly persons; in such cases the prostate appears embedded in the walls of the gut, a disposition fraught with danger to the intestine in the ordinary operation for stone.
The prostate gland varies so much in size at different periods of life, and even in different individuals of the same age, that it is impossi ble to specify its exact dimensions. The organ is small in the child ; it increases greatly at puberty ; in middle age its measurements are still larger, and in the decline of life they become not unfrequently excessive. In the healthy adult subject. the extreme length of the prostate gland from base to apex may be esti mated at from an inch and a quarter to aninch and a half; its.depth at the base seldom ex ceeds one inch, whilst from side to side it measures somewhat more than an inch and a quarter. The urethra traverses the prostate from base to apex, and runs much nearer to the upper than to the lower surface of that body, so that the canal is very unequally surrounded by glandu lar substance. At the base of the prostate the glandular substance above the urethm varies from two to four lines in depth ; below the canal it is upwards of six lines deep ; laterally its thickness may be estimated at about eight lines, whilst in the direction of the ordinary incision in lithotomy, viz. downwards and out wards, from nine to twelve lines is the avemge measurement. Exceptional cases have been reported by Velpeau and others, in some of which no trace of glandular substance existed above the urethm, and in others little or none beneath it; the latter variety might lead to un pleasant consequences in lithotomy.
The prostate gland is enveloped by a dense capsule continuous with the fibrous membrane derived from the posterior layer of the triangu lar ligament of the urethra, and investing the membranous portion of that canal. This cap sule is identified above with the anterior and lateral true ligaments of the bladder, and its strength is such as to impart great firmness to the prostate, and a power of resistance altoge gether foreign to the glandular substance. The anatomist finds it extremely difficult to lacerate the prostate so long as the capsule retains its integrity, but a trifling force suffices to tear or to split the gland after it has been deprived of this covering. The strength of the capsule explains the difficulty experienced by lithoto mists in dividing the prostate gland by the cutting gorget, and was doubtless in great measure the cause of those distressing accidents which so frequently resulted from the slipping of that instrument, and which have led to its disuse in latter years. The common 'ejacula tory ducts traverse the prostate gland from behind forwards and upwards; they are closely approximated to each other, and for practical purposes may be considered to occupy the middle line. It would be impossible to effect with certainty a median section of the gland in the living subject without injury to one or both of these ducts : this constitutes a strong objection to the recto-vesical operation of lithotomy, but they are out of danger in the lateral and bilateral methods.