PERINEUM. 
PERICARDIUM.—See Heart. 
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 vesicule seminales and vasa deferentia; 
inferiorly, the perineum is quite superficial, 
being covered by the integuments only ; and it 
1s circumscribed 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 innominatum, but is in 
reality separated from the bone by the obturator 
infernus 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 ligamentous structures which 
cwcumscribe 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 between the tube- 
rosities of the ischia; and the third stretches 
from the point midwayjbetween the tuber ischii 
and the arch of the pubis, to the centre of the 
great sacro-sciatic ligament of the opposite side. 
In 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- 
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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, 
The posterior triangle is bounded laterally by 
the great sacro-sciatic ligaments, and in the re- 
cent state by the edge of the gluteus maximus 
muscle also. The coccyx usually protrudes 
forwards so much that the area of the posterior 
‘ triangle is less than that of the anterior, not- 
withstanding that the base of each of them is 
represented by the same line. This posterior 
triangle contains the anus with the inferior por- 
tion of the rectum, &c., and is usually called 
the anal division of the perineum. 
It should be borne in mind that the measure- 
ments of the inferior outlet of the pelvis may 
present considerable variations in different sub- 
jects, and that the operator may be obliged to 
modify the length and the direction of his inci- 
sions in lithotomy to suit such cases. M. Du- 
puytren, for example, in twenty-three subjects 
which he examined, found the distance inter- 
mediate between the tuberosities of the ischia to 
vary from two inches to three and a-half inches ; 
and M. Velpeau, who measured forty subjects, 
observed in one case these processes to be but 
an inch and three quarters asunder, whilst in 
another they were four inches apart. 
In order to perform successfully many of the 
operations in this region the surgeon requires 
an accurate knowledge of the axes of the pelvis, 
and to study the modifications which these 
imaginary lines exhibit in childhood and old 
age as compared with adult life. In the full- 
grown male the axis of the superior aperture of 
the true pelvis takes a direction from the vici- 
nity of the umbilicus downwards and back- 
wards to the coccyx, whilst the axis of the infe- 
rior aperture passes upwards and slightly back- 
wards through the mid space between the 
tuberosities of the ischia to the promontory of 
the sacrum; these two lines intersect each 
other in the pelvic cavity, forming an angle 
slightly obtuse and salient posteriorly: the axis 
of the true pelvis (or in other words a line pass- 
ing through the centres of the upper and lower 
apertures respectively) is therefore a curved 
line concentric with the curvature of the sacrum, 
and having its concavity directed forwards and 
downwards towards the symphysis pubis. 
During childhood the true pelvis is imper- 
fectly developed ; ithas but little depth, and its 
