Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/191/
ANUS. 
of the prostate gland and membranous portion 
of the urethra, and converging beneath the 
latter are inserted in common between the bulb 
and the fore-part of the rectum into the central 
point of the perinæum ; these portions in their 
descent present a well-defined edge inwards or 
towards the median line. The middle, or 
aponeurotic portion, is broad and thin above, 
the vesical fascia adhering so closely to it as to 
render its separation difficult. As it descends 
it increases in thickness, expands close to the 
rectum, and is inserted into the coats of that 
intestine, intermingling with its longitudinal 
fibres, and with the sphincter ani ; in the female 
it is intimately attached to the vagina also. 
The posterior or Ischiatic portion passes al¬ 
most transversely inwards, and is inserted into 
the coccyx, and into the cellulo-tendinous line 
which extends from the latter to the rectum ; 
some fleshy fibres are continuous from one 
muscle to the other. This portion of the le¬ 
vator ani is more aponeurotic than the pre¬ 
ceding, and its posterior border is connected to 
the Ischio-coccygæus muscle. The external or 
inferior surface of this muscle is inclined down¬ 
wards, and is more or less related to the obtu¬ 
rator and ischio-rectal fascise, to the glutaeus 
maximus and transverse perinaeal muscles and 
vessels, and to the mass of anal fat. The 
internal or concave surface looks upwards, and 
is closely covered by the vesical fascia, below 
which it is in contact with the rectum, bladder, 
prostate gland, and urethra, or with the uterus 
and vagina. This muscle is disposed on the 
rectum in the same manner in the female 
as it is in the male; the fibres are also inti¬ 
mately connected to the vagina. 
The action of the levator ani muscles is 
two-fold, and not confined to the mere ele¬ 
vation of the anus, as its name would im¬ 
ply. First, they act as a moveable floor to 
the abdomen and pelvis, which can antago¬ 
nize the diaphragm; these two fleshy planes 
being opposed to each other, can, by a slight 
action of one or both, materially alter the 
perpendicular axis of the abdomen, which 
extends between them. This axis is at its great¬ 
est length during the state of expiration, and is 
most diminished when both these muscles are 
forcibly contracting. The levatores ani, how¬ 
ever, have less influence in effecting this change 
than the diaphragm ; they serve chiefly to 
support the lower region of the pelvis and the 
several viscera this cavity contains against the 
combined protruding forces of the diaphragm 
and abdominal muscles in violent exertions of 
the body, or in forcible efforts of respiration, 
or in the evacuation of the contents of the rec¬ 
tum and bladder ; and, secondly, they not 
only raise, but dilate the anus, by drawing out 
its circumference so as to overcome the sphinc¬ 
ters ; at the same time they compress and 
assist in emptying the rectum, particularly the 
dilated pouch, which is a little above the anus ; 
they also resist the prolapsus of the mucous 
coat of the intestine, and raise it after it has 
been to a certain extent protruded by the action 
of the abdominal muscles. They raise and draw 
forward the coccyx after it has been forced back 
179 
by abdominal pressure in parturition, or in the 
ordinary evacuation of the bowels, and further, 
by raising and compressing the trigonè of the 
bladder, they assist in expelling its contents, 
and for the same reason they can also empty the 
vesiculæ séminales of their fluid. The anterior 
portions of these muscles are intimately con¬ 
nected to the membranous part of the urethra, 
and are variously modified in different indi¬ 
viduals and in different animals ; we consider 
those muscular fasciculi which have been de¬ 
scribed differently by anatomical writers under 
different names, compressores urethrae, &c., as 
parts of or appendages to these muscles : these 
urethral portions of the levatores ani can cer¬ 
tainly compress the membranous part of the 
urethra and empty its canal ; they can even 
interrupt or suddenly stop the stream of urine, 
and thus they may occasionally aid the neck of 
the bladder in retaining the contents of that 
organ. 
The Ischio-coccygœi muscles are situated at 
the posterior inferior part of the pelvis ; they 
are thin, flat, and triangular, composed of a mix¬ 
ture of fleshy and tendinous fibres. The apex 
or origin of each is attached to the spine of the 
Ischium, and its base is inserted into all the side 
of the coccyx, and a small portion of the 
sacrum ; they are partly covered by the great 
sciatic ligaments. The superior and posterior 
border is connected to the lesser sciatic liga¬ 
ment, and the anterior border is in part con¬ 
tinuous with the levator ani muscle ; the an¬ 
terior or pelvic surface is connected to the 
rectum and the surrounding adipose substance. 
This pair of muscles appear as a prolongation 
of the levatores ani, and are of use in com¬ 
pleting the inferior boundary of the pelvis; 
they thus support the rectum and the pelvic 
viscera, and they also serve to retain the coccyx 
and restore it to its situation when protruded by 
thediaphragm and abdominal muscles in the pro¬ 
cess of parturition, and in the act of defecation, 
or when drawn too much forward by the levatores 
ani muscles. If the several muscles in this 
region be now partially removed on one side, 
the lower extremity of the rectum will become 
more distinct, and will be found surrounded by 
a quantity of loose, fatty, cellular tissue, sepa¬ 
rating it from the surrounding muscles and 
bones; this contains many nervous filaments 
and numerous bloodvessels, particularly veins. 
(See Intestinal Canal.) Anteriorly in the 
male subject a small triangular space, the 
bulbo-rectal hollow, will now become distinct; 
this is situated between the anus and mem¬ 
branous portion of the urethra ; the base of it 
is at the skin of the perinæum; the apex at 
the prostate: to the last the rectum will be 
seen rather intimately connected. The bulb and 
the membranous portion of the urethra bound 
this space in front, and the rectum behind. 
(See Perinæum and Urethra.) 
Rectum.— In addition to the several muscles 
which have now been severally noticed, and 
which thus serve not only to retain and support 
the rectum and anus, but which even enter into 
the structure of the former, we have further to 
consider the parts more immediately composing
        

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