PERINEUM. 
of the vas deferens becomes continuous with 
that which carpets the urethra at the orifice of 
the common ejaculatory duct. 
The membranous portion of the urethra is 
intermediate between the prostatic and the 
spongy portions of that canal. In situ its 
length seldom exceeds three quarters of an 
inch, but when detached and extended it ap- 
pes about an inch long. Its direction is nearly 
orizontal, but its upper surface presents a very 
slight curve, concave towards the pubis. Its 
under surface is overlapped from before by the 
bulb, a disposition which diminishes somewhat 
the apparent length of its lower wall. Its 
anterior extremity is fixed by the triangular 
ligament of the urethra, a structure of uncom- 
mon strength, through which it passes; but 
erly it projects behind the triangular 
igament for a short distance, and being there 
girded by Wilson’s muscles, which support it 
like a sling, it possesses in that situation con- 
siderable mobility. The membranous portion 
of the urethra is naturally the narrowest part of » 
the canal, presenting in this respect a marked 
contrast to the prostatic and spongy portions. 
Its parietes are endowed with considerable 
agi of resistance, being strengthened in 
ront by the triangular hgament, which sends 
forwards upon them an expansion continuous 
with the fibrous covering of the bulb; whilst a 
still stronger expansion derived from the back 
of the triangular ligament surrounds the urethra 
beneath Wilson’s muscles, and affords it power- 
ful protection posteriorly. Between this latter 
investment and the mucous membrane a pecu- 
liar structure exists of which the exact nature 
is rather doubtful, some considering it a modi- 
fied erectile tissue, whilst others look upon it as 
muscular. 
The membranous portion of the urethra 
merits from the surgical anatomist an attentive 
consideration. It is here that the operator lays 
bare the groove of the staff in lithotomy per- 
formed after the lateral or bilateral methods; 
this is the situation in which spasm usually 
arrests the catheter, the obstruction being pro- 
duced by undue action of Wilson’s muscles. 
Foreign bodies, such as calculi, are very likely 
in consequence of its diminished calibre to be 
impacted in this part of the canal, and its 
anterior extremity is frequently the site of per- 
manent stricture. 
In using a curved catheter the surgeon should 
slacken the penis upon the instrument so soon 
‘as its point has fairly traversed the triangular 
ligament; for if, during the further depression 
‘of the handle, the penis be forcibly stretched 
upon the catheter, its point may push the upper 
‘wall of the urethra against the back of the 
pubis, and in that manner produce considerable 
mischief. It is also of advantage to communi- 
eate a slightly onward movement to the catheter 
this part of the passage, as the bladder is 
Situated much more posteriorly, and in the 
introduction of any instrument, whether curved 
or straight, it should be borne in mind that 
spasmodic obstructions yield in general to gentle 
ut continued pressure, and that attempts to 
ree such strictures are usually productive of 
925 
increased spasm, and, if persisted in, of lacera- 
tion of the urethral canal. 
In connexion with the perineum, so much of 
the spongy portion of the urethra only as is 
covered by the acceleratores urine muscles re- 
quires to be considered, and of this the bulb 
constitutes the largest and most important part. 
The bulb is an oval swelling, in which the 
corpus spongiosum urethre commences poste- 
riorly, it varies in size according to the sub- 
ject, being small during childhood, enlarging 
very much at puberty, and often presenting 
excessive dimensions in old men ; during erec- 
tion, too, it is turgid and swollen, though at 
other times it remains comparatively flaccid. The 
length of the bulb, when well developed, may be 
estimated at an inch and a half, and its thickness 
or depth from the cavity of the urethra at about 
eight lines. Its posterior extremity is thick and 
overlaps the membranous portion of the ure- 
thra, whilst anteriorly the bulb becomes gra- 
dually narrower, but there is no exact line of 
demarcation between that body and the re- 
mainder of the corpus spongiosum. The bulb 
is situated between the crura penis and in front 
of the triangular ligament of the urethra, to 
which it is connected by the expansion of 
fibrous membrane already described ; it is co- 
vered by the acceleratores urine, and derives 
from them a muscular sheath all but perfect. 
The bulk of this body is constituted by a 
spongy erectile tissue, remarkably soft, and 
possessing intrinsically little powers of resist- 
ance, but a thin fibrous membrane of invest- 
ment affords 1t some protection from without. 
The canal of the urethra in this situation pre- 
sents a slight dilatation (most observable infe- 
riorly) named the sinus of the bulb, and the 
delicate ducts of Cowper’s glands, two in num- 
ber, open into the lower and lateral parts of the 
passage still further forwards. It should be 
particularly noted that the bulb, measured at 
the exterior, is in point of size quite out of 
proportion to the width of the corresponding 
part of the urethral canal, the canal presenting 
but a slight dilatation, whilst the dimensions of 
the bulb are very considerable; and of equal 
importance in practice is the fact that the axis 
of the bulb differs widely from the axis of the 
corresponding portion of the canal, the axis of 
the bulb running in a very oblique direction 
downwards and backwards towards the lower 
extremity of the rectum, whilst the axis of the 
canal lies upon a higher. plane and runs much 
more nearly horizontally backwards. 
In a healthy urethra the principal difficulties 
of catheterism, whether performed by straight 
cr by curved instruments, are encountered at 
this part of the passage: the sudden change 
in direction which the urethra here undergoes, 
the abrupt narrowing of the membranous por- 
tion immediately behind the dilatation of the 
bulb, the mobility of the urethra in front of 
the triangular ligament, and its immobility 
where it passes through that structure, the ease 
with which a catheter perforates the delicate 
tissue of the bulb, and, above all, the striking 
difference in direction observable between the 
axis of the bulb and the axis of the correspond- 
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