PERINEUM (in Surgical Anatomy).—The perineum (in the general acceptation of that term) is one of the names applied by anatomists to the extensive region which contains the lower part of the rectum intestine, together with a portion of the genito-urinary organs and their appendages, and of which the circumference corresponds in a great measure to the periphery of the inferior aperture of the pelvis ; in the pre sent article, however, it is intended to describe the perineum in the male subject only, as the parts which it comprises in the female are no ticed in detail under other headings in this work.
The limits which we would assign to this region are sufficiently precise : superiorly, or towards the abdominal cavity, it extends as far as the reflections of the recto-vesical layer of the pelvic fascia and the great cul-de-sac of the peri toneum, including within its precincts the pros tate gland and the neck of the bladder, together with a part of the inferior surface of that viscus and the vesieulte seminales and vasa deferentia; inferiorly, the perineum is quite superficial, being covered by the integuments only ; and it is circurnscribed partly by the fixed boundaries of the inferior aperture of the pelvis, and partly by the obturator fascia, an aponeurotic expan sion which appears to line a portion of the inner surface of the os innorninatum, but is in reality separated from the bone by the obturator internus muscle and the internal pudic vessels and nerve.
In describing this complicated region it will be advantageous to consider in the first place the osseous and lig,amentous structures which circumscribe the inferior outlet of the pelvis, and to notice in a general manner the course of the rectum and urethra, together with so much of the urinary bladder as is connected with the perineum, for in the sequel it will appear that the rectum and the urethra are the principal elements of the region, and that almost all the other parts contained in it are appendages of either the one or the other, so that by the adop tion of this method a key to the anatomy of all the subordinate structures will be obtained.
The inferior aperture of the male pelvis exa mined after the removal of the soft parts (the sacro-sciatic ligaments being preserved) is dia mond-shaped ; it is limited anteriorly by the arch of the pubis, posteriorly by the extremity of the coccyx, and laterally by the rami of the pubis and ischium, the tuberosity of the ischium, and the great sacro-sciatic ligament at each side respectively. It preSents three diameters, viz. the antero-posterior, the transverse, and the oblique. The first extends from the coccyx posteriorly to the symphysis pubis in front '; the second passes transversely beoseen the tube rosities of the ischia; and the third stretches from the point midwayibetween the tuber ischii and the arch of the pubis, to the centre of the great sacro-sciatic ligament of the opposite side. ln a well-formed male pelvis these three diame ters are almost equal, being each of them nearly three and a-half inches in extent; but in conse quence of the mobility of the coccyx that bone may be moved backwards considerably, and under such circumstances the antero-posterior diameter becomes increased to a corresponding. amount.
This large space admits of a very natural division into two triangles, one in front, the other posteriorly ; the base of each respectively corresponds to the line passing transversely be tween the tuberosities of the ischia, and the apex of the one is formed by the arch of the pubis, whilst that of the other is constituted by the extremity of the coccyx.
The anterior triangle is equilateral ; its sides are formed by the rami of the ischium and pubis, and are each from three inches to three and a-half inches in length ; it contains the urethra and the root of the penis, with their appendages, and may be named the urethral division of the perineum.