Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Todd, Robert Bentley
URETHRA. 1247 
the prostatic part of the urethra gradually de¬ 
scends, until its general direction is more con¬ 
tinuous with that of the membranous part. 1 
shall defer the description of the caput gal- 
linaginis until I come to that of the general 
surface of the urethra. 
The connection of the urethra to the pro¬ 
state is very close, the ducts of the gland 
passing directly into it ; it is therefore im¬ 
possible to raise it from its attachment without 
division of the prostatic ducts. When a ca¬ 
theter is introduced, the course of the canal 
invested by the prostate can be indistinctly 
traced by the finger introduced into the 
The membranous portion (pars muscularis, 
isthmus urethrce) commences from the anterior 
part of the prostate, and extends beneath 
the arch of the pubis as far as the bulb : it is 
included between the prostatic and spongy 
portions, and is covered slightly at its anterior 
and under part by the bulb, so that it is 
really shorter below than above. It makes a 
slight curve, the concavity facing upwards. 
The concavity is at the distance of nearly an 
inch from the interpubic substance ; the con¬ 
vexity looks towards the perinæum. Be¬ 
tween it and the pubis, and just beneath the 
pubic arch, the dorsal veins of the penis run. 
Proceeding from the anterior extremity of 
the prostate, the membranous portion of the 
urethra traverses the triangular ligament, 
which splits into two lamellae : one passing 
backwards over the prostate, is continuous 
with the capsule of the gland, the other ad¬ 
vances forwards over the bulb, and blends 
with the tendinous investment of the spongy 
body. The opening through which the ure¬ 
thra passes is round. The membranous por¬ 
tion forms the segment of a circle, whose 
radius is, according to Krause, 2i lines. This 
part of the canal has been termed membran¬ 
ous, from the idea that it represented a simple 
membrane when deprived of its surrounding 
muscular structure, and that it was wholly 
destitute of any investment of the spongy 
body. This, however, is not correct ; there is 
a thin layer of vascular tissue, continuous in 
front with the spongy body, and closely sur¬ 
rounding the mucous membrane of this part 
of the urethra, between it and its muscular 
layers. The vessels of this extension of the 
spongy body pass backwards, to terminate in 
the plexus surrounding the neck of the blad¬ 
der : this is mixed up with elastic tissue, and 
constitutes a truly erectile tissue. An exten¬ 
sion of the same structure enters into the for¬ 
mation of the caput gallinaginis. 
Between the layers of the triangular liga¬ 
ment, and in close connection w'ith the mem¬ 
branous part of the urethra, are found three 
sets of muscular fibres (mus cuius urethralis) : 
they consist of the two pairs of muscles de¬ 
scribed, one by Wilson and the other by 
Guthrie ; and the circular fibres of Santorini, 
which closely surround the urethra. The 
anteprostate, or Cowper’s glands, covered by 
the inferior stratum of the compressor urethrae, 
are placed beneath this part, and the arteries 
of the bulb are in close approximation to it, 
running beneath and on either side of it. The 
floor of the membranous portion is traversed 
longitudinally in the median line by the pointed 
end of the caput gallinaginis. 
If a catheter be passed into the bladder, 
the membranous portion can be distinguished 
by the finger introduced into the rectum and 
drawn forwards, there being only a small quan¬ 
tity of cellular membrane interposed between 
the under part of its muscular investment and 
the intestine. 
Boyer estimated the length of the mem¬ 
branous portion at about 1 inch ; Ducamp 
from 9 to 10 lines ; Lisfranc found it in twelve 
subjects to vary from 7 to 11 lines. In these 
its anterior diameter varied from 3£ to 
lines, its posterior from 4j to 5 lines, and just 
behind the bulb it measured at least li line 
less than in any other part. It is universally 
admitted that the point of junction between 
the membranous and spongy portions is the 
narrowest part of the urethra, with the excep¬ 
tion of the meatus. 
The membranous part of the urethra is sur¬ 
rounded by muscular fibres, which have been 
variously described by different anatomical 
writers. Thus Santorini, as early as 1724, in 
his Observationes Anatomicæ, pointed out some 
transverse fibres as encircling the urethra at 
this part: he terms them “ the elevator or eja- 
culator urethrae,” and describes them as being 
inserted into the lower part of the urethra. 
Mr. Wilson, in the year 1808, gave a descrip¬ 
tion of two muscles surrounding the mem¬ 
branous part of the urethra, the origin of 
which is from a tendon attached to the pos¬ 
terior part of the symphysis pubis, a little 
above its lower border: the muscle thus arising 
from a single origin then descends, and divides 
into two portions, which, reaching the mem¬ 
branous portion of the urethra, spread them¬ 
selves out by its side, and are implanted into 
a common tendon below it. The muscle is 
termed by Wilson the compressor urethrae. 
In 1834, Mr. Guthrie, in his lectures at the 
Royal College of Surgeons, demonstrated 
another series of muscular fibres, as sur¬ 
rounding the membranous portion of the 
urethra, and of which he considers Wilson’s 
muscle as a part. That portion described by 
Guthrie, and now known by his name, arises 
by a thin tendon on either side, from the ra¬ 
mus of the ischium, and, passing transversely, 
splits into two portions, one above and the 
other below the urethra; the two muscles 
are connected together above by a mesial 
tendon, which, passing forwards, is inserted in 
part into the upper part of the urethra, whilst 
another portion, passing backwards, is im¬ 
planted into the upper surface of the front of 
the prostate. The under portion of the muscle 
is also connected with its fellow bjr a similar 
mesian tendon, which, advancing forwards, 
goes to the central tendon of the perinæum, 
and, sending a slip backwards, is inserted into 
the under part of the prostate. 
The muscles are included between the two 
layers of the triangular ligament ; and the


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