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The levator ani muscle; Its structure in man and its comparative relationships.

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THE LEVATOR AN1 MUSCLE; I T S STRUCTURE I N
MAN, AND I T S COMPARATIVE RELATIONSHIPS
WILBUR C. SMITH
Department o f Anatomy, Tulane University of Louisiana School of Medicine
FIVE FIGURES
F o r the last half century the levator ani muscle has claimed
the attention of various writers, who have been, almost wholly,
attracted to its study by the surgical importance of the general
region whicli it occupies.
Owing t o the difficulties which are met with in the exposure
of this muscle in routine courses in anatomy, a complete
understanding can be gained only by special dissections made
a t the sacrifice of other structures. Recognizing this fact,
many authors have made such special dissections of the perineum, but, as I point out later, abnormal female perinei have
been described as normal. Artifacts due to parturition have
not been recognized as such.
The primary objective of the writer is t o present the comparative results of dissections of nulliparous and parous
women. Secondarily, information concerning the levator ani
of the male and the directions of the perineal openings in both
sexes receive consideration. Lastly, there is incorporated a
survey of the literature relating to the subject, not only from
the standpoint of practical applications, but also including
the comparative relationships of the levator ani muscle in the
entire vertebrate group.
I am deeply indebted to Dr. Howard Hill, of Kansas City,
Missouri, for his very valuable suggestions and advice concerning the preparation of this paper, also t o Joseph Sciami
and Wallace P. Sheely, both medical students in Tulane Uni175
THE ANATOMICAL RFCORD, VOI.. 26, NO. 3
OCTOBER.
1923
1‘76
WILBUR C. SMITH
versity, for drawings and assistance in dissection, respectively. I am very grateful for their kindly cooperation.
I n 1555 Vesalius wrote an account of the levator ani of man
under the name of ‘musculus sedum attolens, ’ which description was adopted and retained until recent years. During tlie
last half century, dne to the frequrnt impairment of its function in the female and to the advaricement of modern surgery,
it has claimed tlie attention of various writers more than any
otlier single muscle of the body. Recently it has been studied
quite extensively in the lower vertebrates and gradually its
divisions in man, wliicli a r e similar to the corresponding
muscles in otlier vetebrates, a r e becoming more generally
recognized.
I have found the literature bearing upon the levator ani
muscle not only voluminous, but very conflicting, particularly
so in those publications dealing with the female perineum.
Tlie confusion arises not only from lack of actual familiarity
with the muscle, but also from failure to realize that portions
of its insertion a r e very seldom the same in any two subjects
and from the fact that so many different names have been
given its various divisions. Wit11 the hope that it may be of
general interest and of some convenience, I here include descriptions of the muscle as found in a number of the papers
~ h i c hhave been available.
Paramore begins with the lowest vertebrates in wliich ail:evidence of the pelvic floor is indicated, and carries his investigation from fishes through amphibians and reptiles.
I n fishes, where the pelvis is rudimentary, a pelvic diaphragm can scarcely be said to exist. A considerable advanzement of the pelvis is noted in the amphibians. I n the salamander the ileum has reached and has become attached to the
rib of the single sacral vertebra by a n articulation, thus allowing a to-and-fro movement upon the spine. I n Menobranclius
this upgrowth has remained incomplete, so that the pelvis is
freely movable.
T H E LEVATOR A N 1 MUSCLE
177
I n both Menobranchus and the salamander evolutionary
advance trended toward the fixation of the pelvis to the vertebrae, although this is completely attained only in the latter.
This fixation is associated with progressively greater variations of internal pressure, owing to increase in the general
bodily activity of the higher forms.
In reptiles the sacral vertebrae are present and connecte,tl
with each other by fibrous tissue. The pelvis is completed inferiorly by the juncture of the pubic and the ischial bones,
which may form a median syniphysis. I n Iguana the caudopelvic muscles are very well developed. Instead of a single
caudo-pelvic muscle, as in some other lower vertebrates, two
a r e found on each side. The larger and the most superficial
a r e situated on each side of the cloaca, dorsal to which their
medial borders a r e in apposition. The recti, transversalis,
and the two oblique muscles are present.
A comparison of the anatomical conditions in reptiles, the
Iguana, with those in the salamander, coupled with a consideration of their habits and mode of life, indicates that the
advance in structure is due to a n increase in the general activity and to the change in respiration. The crocodile presents more advanced structures than the Iguana, although
the caudo-pelvic muscles are not so greatly developed. Here
the pelvis is ankylosed to the spine, a circumstance which is
coincident with diminished utility of this musculature. I n the
European tortoise a caudo-pelvic muscle (pubo-coccygeus)
is present on each side, together with the sacro-coccygeus.
The evolutionary series, through the fishes, the amphibians
and the reptiles, suggest that the muscles occluding the pelvic
outlet exist f o r the most part wholly for a pressure effect.
Lartschneider, who extended his investigation through the
order of Mammals, says, “the levator ani in man has originated by the fusion of two separate paired tail flexor muscles
like those of the short and the long-tailed apes and of the
dog,” namely, the pubo-coccygeus and the ilio-coccygeus,
both of which can be readily recognized.
178
WILBUR C. SMITH
Within every order of mammals the pelvic muscles of the
different species show certain interesting relationships. Certain peculiarities occurring in the arrangements and development of the pelvic muscles in any species a r e present in the
case of all other species of the same order. Variations from
this a r e due to the retrogression of the tail part of the long
vertebral column characteristic of such mammals as the Edentata (ant-eaters). The more primitive members of any
order of mammals show a greater separation of the pubococcygeus and the ilio-coccygeus from each other than is seen
in the less primitive.
To begin with, the great skin muscle (cutaneus maximus)
must be clearly considered. I n tlie case of the rabbit this
muscle forms a large circular sack, situated immediately under the skin and enveloping nearly the whole of the body.
The fiber-fasiculi of this muscular sac extend into the caudal
end of the body, from the lumbar and the abdominal region,
over the two nates to the median line of the dorsal surface of
the tail, where they insert themselves almost quite up t o the
tail tip. Some fibers issue from this great skin muscle, forming a broad, rather strong, ligament-like muscle which runs
forward past the rectum to become attached to the corpuscavernosum penis, almost, if not quite, to the tip of the latter.
These fibers represent the pubo-coccygeus muscle of the rabbit. Likewise, the bulbo-cavernosus, the ischio-cavernosus,
and the external sphincter have the same origin. The dissection of the pelvic cavity of the rabbit, from within outward,
shows that the obturator internus lies on both sides of tlie
rectum throughout its entire course in the pelvic cavity.
I n the higher mammals the greater part of the cutaneus
maximus draws itself more and more from the caudal half of
the body toward the head, until in man it is only represented
by the platysma and some of the skin muscles of the face. On
the other hand, those parts which the great skin muscle sends
off to the end of the alimentary tract and to the external
genital apparatus remain in the higher vertebrates as muscles
THE LEVATOR AN1 BIUSCLE
179
apparently quite foreign t o it and independent even after disappearance of the chief bnlk of the parent muscle, namtly,
the pubo-coccygeus, sphincter ani, bulbo- and ischio-cavernosus.
I n the ant-bear (Myrmecophaga tamandua) the pubo-coccygeus arises from the body and the descending ramus of the
pubis and runs dorsocaudally t o gain its insertion upon the
ventral surface of the first coccygeal vertebra. I n the Marsupialia, Carnivora, Prosimiae, and the Primates, the pubococcygeus takes origin a t the linea terminalis of the pelvic
outlet in the region of its ventral third. I n certain Primates
(Macacus maurus, Cynocephalus mormon, Troglodytes niger )
the attachment of the pubo-coccygeus moves down to the lateral wall of the small pelvis until eventually it reaches that
point of attachment common to the orang-outang and man. I n
these the dorsal end of this musele has completely separated
from its equivalent in the rabbit, and in the case of the longtailed Edentata, Marsupialia, Carnivora, Prosimiae, and
Primates is inserted to the lateral border and the median and
ventral surfaces of the tail near the last coccygeal vertebra.
I n Edentata, Marsupialia, Carnivora, Prosimiae, and tailed
Primates, the pubo-coccygeus is a separate muscle, which
arises from the back of the 0 s pubis and inserts itself upon the
ventral surface of the tail root. These muscles are separated
by a large cleft for the external sphincter, the bulbo- and
ischio-cavernosus.
I n the muscles of the pelvic outlet of the Ungulata (roe and
horse), one encounters a powerful external sphincter, which
passes ventrally to the bulbo-cavernosus, and from the fusion
of these fiber-fasciculi pass t o the root of the penis. On the
lateral side of this mass there arises a broad Iigament-like
muscle which fastens itself to the lateral wall of the true
pelvis. This ligament-like muscle corresponds to the pubococcygeus of the Edentata, Marsupialia, Carnivora, Prosimiae, and the Primates, except that a few fasciculi run into
the fascia of the tail and that its origin extends farther dor-
180
WILBUR C. SMITH
sally. It functions as a suspensory muscle of the rectum. The
pelvic inclination in the Ungulata and the attachments of the
muscles back as f a r as the coccygeus allow no other function.
I n the Ungulata those muscles which have split themselves off
from the cutaneus maximus a r e situated around the end of
the intestinal tract and the external genitalia. I n the Edentata, Marsupialia, Carnivora, Prosimiae, a ligament-like
band separates itself on both sides as the pubo-coccygeus.
From this muscular mass the band passes from the pelvic outlet along the lateral pelvic wall into the pelvic cavity and functions as a flexor of the tail root. While the pubo-coccygeus of
man, as of other mammals, must be considered as having been
derived from the cutaneus maximus, the ilio-coccygeus belongs to that group of skeletal muscles found on the ventral
surface of the tail part of the vertebral column.
I n the Ungulata one finds powerfully developed skeletal
muscles on the ventral surface of the sacrum. These act as
flexors, and vary correspondingly with the development of
the tail. There result numerous variations, of which the horse
and roe show opposite extremes. Laterally the caudal flexors
reach the lateral pelvic wall and continue to broaden. From
the ischium, they move u p t o the ileum, and finally separate
themselves from the chief mass into independent muscles, the
ilio-coccygei. This is beautifully demonstrated in the shorttailed Edentata.
I n the long-tailed Edentata t h e e flexors a r e found on each
side, lateral, medial, and intermediate. These run side by
side to gain their insertion into the ventral surface of the tail
nearly as far a s the tip. I n the Marsupialia the intermediate
flexor has withdrawn from the caudal fourth of the tail, but
in the Carnivora, Prosimiae, and the Primates, when the vertebral column retrogrades, the lateral and the medial flexors
disappear leaving the ilio-coccygeus much the more prominent.
I n man the ilio-coccygeus forms a part of the pelvic diaphragm, and the flexor caudae medialis and lateralis, which
THE LEVATOR A N 1 MUSCLE
181
a r e so prominent in the lower vertebrates, remain as fiberfasciculi, the sacro-coccygei anteriores.
The pubo-coccygeus, i n the Carnivora a separate muscle, is
a flexor of the tail root, which was a t one time a part of the
cut aneus maximus.
I n short-tailed Primates the flexores caudae medialis and
lateralis have atrophied to thin fibrous bands, leaving the iliococcygeus to predominate. The pubo-coccygeus in its dorsal
part becomes tendinous, and, on the point of casting off its
intimate relations to the tail part of the vertebral column, it
separates itself into fibers which for the greater part pass to
the median line to blend with those of the opposite side. The
tail flexor muscles, grouped in pairs, join or fuse to form the
pelvic diaphragm and close the pelvic cavity at its outlet.
Now, in the short-tailed Primates, as already mentioned, these
muscles gradually lose their relation to the tail part of the
vertebral column and unite by means of tendinous portions to
the coccygeal vertebrae and with the muscle of the opposite
side. They form an unpaired muscle, stretched out in a transverse direction and closing the pelvic outlet.
In the chimpanzee, the retrogression of the tail part of the
vertebral column has reached its highest degree. The caudal
end of the tail approaches the pelvic outlet. The flexor
muscles, which previously a r e grouped in pairs, now unite to
form one, the diaphragm of the pelvis. The pubo-coccygeus
of the chimpanzee is a ligament-like muscle and arises on
each side by means of tendon fibers from the line& terminalis,
and passes with its medial border next to the rectum, behind
which the two muscles unite and gain attachment to the ventral surface of the coccyx and the last sacral vertebra. The
ilio-coccygeus has become altered with the concurrent reduction of the tail. It still arises on both sides of the pelvic cavi t y ; i t is reduced to a delicate thin muscle whose fibers extend
fan-like from their origin, terminating in a fibrous tendon,
the ventral border of which rests upon the pubo-coccygeus.
The coccygeus is in its greatest part transformed into a ten-
182
WILBUR C. SMITH
don, so that now one finds that, after the atrophy of the visible
tail muscles, which were once flexors of the tail, the pubococcygeus and the ilio-coccygeus join together t o form an unpaired muscular sheath, which stretches itself out in the bony
frame of the pelvic outlet, being perforated by the rectum,
the vagina, and the urethra.
Going further in the series of the anthropoids and comparing the pelvic diaphragm of the chimpanzee with that of the
orang-outang, one finds a gap a s great as that between the
chimpanzee and man. The pelvic diaphragm of the orangontang is nearly of the same grade of development as that of
man. Kohlman writes regarding the levator-ani of the
Chimpanzee: “The dorsal portion which in tailed apes is
present in great strength is transformed into a fascia. Of the
levator there is still only the ventral and lateral original portion.” Rudolf Pick states that the levator-ani of the orangoutang is much extended, especially the posterior fasciculi and
the ischio-coccygeus, but in essentials does not differ from
that of man.
Lartschneider has called attention t o the bearing of the upright position upon the origin of a pelvic floor. He regards
its development as a natural consequence of changed position
of the body. The pelvic outlet of man, by virtue of his upright position, is directed almost downward ; the diaphragm
a t the base stretches itself out, hence closing the outlet on
which the pelvic organs in part rest.
The dorsal part of the pelvic floor in the chimpanzee consists of the fibrous ilio-coccygeus, which, due t o the position
of the pelvis, forms a part of pelvic roof. This is in contrast
to the condition in man where it forms a visceral support in
the pelvic floor. The levatores consist of two portions, the
ilio-coccygeus and the pubo-coccygeus. The f ormer belongs
to the vertebral column musculature, being the remnant of the
flexor tail muscles (flexor caudae medialis and lateralis), or
sacro-coccygeus of man. The pubo-coccygeus of man is traced
back to the great skin muscle, the cutaneus maximus.
THE LEVATOR A N 1 MUSCLE
183
Lartschneider suggests that it would be advisable to describe the levator ani as follows: “It is subdivided into two
portions, portio pubica and portio iliaca. The portio pubica
arises as a thin muscular layer on both sides of the symphysis pubis, extending outward as far as the entrance inta the
obturator canal. The fibers a r e directed backward at the
sides of the rectum and converge behind it where the medial
fibers cross and form a loop. The fibers which, on both sides,
arise more laterally from the pubis are directed toward the
coccyx and a r e inserted by means of a common tendinous
aponeurosis to the second, third, and fourth coccygeal vertebra. Between the coccyx and the tendinous aponeurosis
there exists a space exactly in the midline which is filled partly
with f a t t y tissue and which serves as a passage for the nerves,
venous plexuses and the end of the middle sacral artery.
“The portio iliaca arises in the continuation of the line of
the origin of the pubic portion as f a r as the ischial spine, to a
greater extent from the obturator fascia and to a smaller extent behind this from the medial surface of the ischium. The
most posterior fibers a r e inserted into the lateral border of
the last coccygeal vertebra, whilst the fibers in front of these
a r e attached to the raphh, which extends from the tip of the
coccyx to the a ~ i u s . By this raphd the portio iliaca of one side
is joined with that of the opposite side to form a muscular
plate stretched obliquely behind the portio pubica” (literal
translation),
Thompson states that Lartschneider ’s views of the levator
have not been adopted by succeeding writers. As noted above,
the latter applies the terms portio pubica and portio iliaca to
the levator divisions in man and other mammals. Thompson
asserts that, since the ilio-coccygeus in man represents the
ventral fibers only, the pubo-coccygeus includes the puborectalis. The portio pubica of the levator ani is not exactly
the pubo-coccygeus in mammals generally.
Thompson states also that neither the ilio-coccygeus nor the
pubo-coccygeus are present i n the Ungulata, and that the view
of Lartschneider, concerning the origin of the pubo-coccygeus
184
WILBUR C. SMITH
from the cutaneus maximus was based upon observations confined to the rabbit. It appears that the superficial sphincter
of the rabbit was mistaken by Lartschneider for the pubococcygeus. Holl likewise makes this interpretation, and in it
also states that Lartschneider 's conclusions are incorrect.
I n the camel there are two muscles which arise from the internal surface of the ischium, one close to the spine ancl one,
more ventral, close to the obturator foramen. The latter
passes along the lateral aspect of the rectum to terminate in
short tendinous fibers in its walls near the anus, none being
attached to the caudal vertebrae. HoH calls the dorsal muscle
the ilio-coccygeus and the ventral muscle the pubo-coccygeus,
while Thompson and Lartschneider hold that the dorsal
niuscle is the ischio-coccygeus and the ventral the pubo-coccygeus. Lartschneider thinks that the ventral muscle is the
pubo-coccygeus of man. Thompson raises the question as to
which of the flexor tail muscles it corresponds-the ilio-coccygeus or the pubo-coccygeus, or both.
Paulet (as quoted by Hogge), writing on comparative
anatomy of the perineum, stated that the ischio-anal muscle
in the stag is homologous with the levator ani of man, but
that it differs from i t in form. H e regards the muscIe as
corresponding only to a limited part of the levator ani, to
that p a r t which remains if the fibers from the pubic ancl obturator fascia be removed.
Hogge, i n investigating the muscles of the perineum, used
human embryonic material, but his method of investigation
was that of serial sections, and he did not study the adult
anatomy, to which his method could not be applied. Hogge
points out that it is well, however, to remember that in the
foetus at term and in the young child the intra-pelvic organs
do not occupy exactly the same position as in the adult. F o r
example, the anus is more superficially placed in the foetus.
The bladder in the foetus and in the child lies well above the
superior border of the symphysis pubis. It is more vertically
placed in the child, not reaching the pelvis until about the
age of eight years.
THE LEVATOR A N 1 MUSCLE
185
P e t e r Thompson, who perhaps has done more work on the
muscle than any of the past o r present generation, described
it ( ,OO) as follows :
“The levator ani in the human subjects arises along a n interrupted line from the back of the body of the pubis, from
the pelvic fascia on the side wall of the pelvis and from the
spine of the ischium; its fibers a r e inserted into the coccyx
and the ano-coccygeal raphe, while a few pass to the central
point of the perineum. I t is clear, therefore, that most of the
fibers at their insertion a r e post anal.
“Ilio-coccygeus arises from the pelvic fascia and from the
inner aspect of the spine of the ischium. I t s attachment to
the pelvic fascia is along a curved line whose concavity is directed upward. The line has a varying relation to the side
wall of the pelvis ; in some cases it is situated almost as high
as the obturator canal, and in other cases considerably below
it. Posteriorly the origin of the ilio-coccygeus extends as far
as the margin of the great sacro-sciatic notch, whilst anteriorly its limit is not always easy to determine. It reaches
almost as f a r a s the commencement of the obturator canal,
and f o r those cases in which there is no clear separation between the ilio-coccygeus and the pubo-coccygeus. The fibers
a r e directed downward, backward and inward to the coccygeal vertebrae. They a r e inserted from behind forward into
the lateral margin of the last two of the coccyx, into the tip
of the coccyx to the posterior margin of the same. A t their
insertion the fibers a r e not all on the same plane, but have a
series of layers superimposed upon each other, the upper
layer consisting of fibers from the posterior end of the muscle.
The middle layer consists of fibers from the muscle of both
sides which decussate without forming a raphe, whilst the
most inferior forms a tendinous raphe in which most of the
fibers terminate.
“The pubo-coccygeus invariably arises from some part of
the pubis: in man from the back of the body of the pubis
along a n oblique line which extends from the lowest limit of
the symphysis upward and outward toward the obturator
canal. Also from the obturator fascia for a limited extent
along a line continued forward from the origin of the iliococcygeus. The limits of the two muscles at this point arv
often difficult to define. The fibers form a flat band about one
186
WILBUR C. SMITH
inch wide, thick on its medial border, thin where it overlaps
the ilio-coccygeus, it is directed backward almost horizontally
along the side of the canal toward the coccyx and sacrum to
which it obtains attachment. Between the tip of the coccyx
and the anus the two pubo-coccygeus come together and form
a thick fibro-muscular layer lying on the raphe formed by the
ilio-coccygeus, nearly all of the pubic fibers pass backward to
the vertebral column. They are joined behind the rectum by
the corresponding fibers of the opposite side and becoming
tendinous form a thick aponeurosis which is continued upward in front of the coccyx and divided into two lateral por
tions which have been named the ligamenta sacro-coccygea
anteriora and a r e fastened to the lower part of the sacrwn
and the upper p a r t of the coccyx; a few of the pubic fibers
pass inward to the central point of the perineum, descend in
close contact to the walls of the rectum and terminate in +lip
external sphincter ani and the skin of the anus. The obturator fibers form the outer border of the muscle and becoming
tendinous join with the ligarnentum sacro-coccygeum anterius. A few decussate in the midline and lie on the upper
aspect of the thick tendinous aponcurosis which constitutes
the chief insertion of the pubo-coccygeus.
“Pubo-rectalis: arises from the back of the lowest part of
the synipliysis pubis under cover of the pubo-coccygeus, from
the upper layer of the triangular ligament and from the pubis
immediately below the symphysis. From this origin the fibers
pass around the lower p a r t of the rectum and, meeting with
thcl fibers of the opposite side, form a strong loop, or girdle
which slings the rectum u p to the symphysis.”
Holl refers to this division as the best-developed muscle of
the perineum. Henle, in describing the pelvic diaphragm,
considers this the only muscle of the levator ani.
Thompson states that the ilio-coccygeus is a degenerated
muscle in man. Paramore replies to this statement with the
observation: “ I n the tailed apes the levator attains a thickness of 5 mm.; in anthropoids it is thin and almost transparent,” and he asks, if it is a degenerated and unnecessary
muscle, why is it present in man and absent in the mare and
the cow. Furthermore, if atrophy has commenced in certain
anthropoids, why has it not reached a higher development in
THE LEVATOR A N 1 MUSCLE
187
m a n ? Holl states that i n the dog and the cat the pelvic diaphragm is composed of the pubo- and the ilio-coccygeus. I n
tailless apes one finds a n abductor caudae, but the ilio-coccygeus is lacking.
Berry Hart published his own researches on the anatomy of
the female pelvic floor, followed by a more extensive work
relating to the topographical and sectional anatomy of the female pelvis. Berry H a r t and Dr. Henry Coe, in speaking of
the pelvic floor, state that it includes both the bladder and the
rectum. It seems, in looking over the literature published
since this time, that many of the authors make mention of this
statement, and all offer the same objection, namely, that if
the bladder is a p a r t of the pelvic diaphragm, it at times rises
up to the umbilicus in distention. The writer is confident that
both Coe and H a r t had in mind just that portion of the bladder which is in direct contact with the levator ani. Meckel
considers the levator as consisting of one undivided muscle in
the male, but divides that of the female into two parts. Testut divides the insertion of the levator ani into three sets of
fibers : post-rectal, lateral rectal, and pre-rectal, claiming with
Cruveilhier and Thompson that the lateral rectal fibers a r e
lost in the longitudinal muscular fibers of the wall of the rectum itself, while Kalischer considers the levator as one muscle
and identifies three sets of fibers in it, pre-rectal, rectal and
post-rectal. Savage, to whom we a r e greatly indebted for his
beautiful work on the female perineum, divides the levator
into the pubo-coccygeus and the obturator-coccygeus, and
Symington and Raney accept the divisions as named by Savage. Cruveilhier and others consider that the anal sphincter
and the levator ani act a s one muscle; they separate its fibers
into vesico-rectal fibers, pre-coccygeaI, coccygeal and sacral
fibers. Rour (as quoted by Hogge) treats the levator ani as
consisting of a superficial and a deep part, the former including only about one-half of the generally accepted insertion;
the latter he states is the levator proper. In a diagram he
shows the deep fibers passing in front of the rectum. Poirier
188
WILBUR C!.
SMITH
and Cliarpy separate the levator into two portions, a superficial external part and a deep portion, internal or elevating.
According to the investigations of Sqppey, Kahbrausch,
Luschka, Lesshaft ( a s quoted by Hogge) and Meriel, the
levator ani is made up of the anterior, middle, and posterior
bundle of fibers. Holmes describes the levator as a muscle of
continuous origin, but defines two insertions. H e suggests
that the name, levator ani, should be changed to tensor
peronei. Dickinson speaks of the levator ani as a horse-shoe
muscle, and for its insertion, like Luschka, describes three sets
of fibers, and Robinson accepts Dickinson as to this shape
and describes an origin from three separate points. Doran
describes the levator a s consisting of two divisions, the pubococcygeus and the ilio-coccygeus, but in the specimen he describes the ilio-coccygeus is not such as one finds in a normal
subject. Harrison does not consider the levator ani as taking
any part in the formation of the perineum. Browning asserts
that in his investigations of the male and the female perineum
of tlie lower animals and of man, he invariably found that
the levator ani is the better developed in the male. This can
readily be explained from the fact that in the male the intraabdominal pressure is greater. H e divides it into the pubococcygeus, fibers coming from the ischial spine, and intervening fibers. Eckley divides the insertion of the levator ani
into three sets of fibers, but gives them no name. Goffe describes tlie levator ani as one continuous muscle, stating that
it arises from the entire circumference of the bong pelvis and
is inserted into the tendinous center known as the perineal
raph6. Marcey claims that the levator ani is inseparably
blended with the sphincter ani. H e treats it as one muscle,
stating that the use of names employed by modern text-books
leads to confusion. Derry, Elliott Smith, and Keith speak
of the levator as consisting of two portions, namely, the pubococcygeus and the ilio-coccygeus; but Derry says that the
white line so commonly spoken of is composed of the tendinous fibers of the levator ani muscle itself. Rtuddiford separ-
THE LEVATOR AN1 MUSCLE
189
ates tlie inserting fibers into three sets, as Sappey, Kahbrauscli, Luschka, Lesshaft and Meriel have done, namely,
the anterior, the middle, and the posterior. But Studdifortl
states that the fibers running behind the vagina a r e composed
almost entirely of involuntary muscle, as proved by the
microscope. He has taken for examination fibers of the internal sphincter ani, or part of the rectal mall. I can find on
microscopic examination no evidence of involuntary muscle.
Harrison bakes up the levator ani into three sets of fibers, the
pubo-coccygeus, the ilio-coccygeus, and the pubo-rectalis. In
1923, Frank, i11 his description of the anatomy of the pelvis,
speaks of the muscles thus : “The pelvic outlet is closed by a
thin but strong musculo-f ascial diaphragm, called the levator
plate, cornposed of the two levatores ani and the two coccygeus
muscles. ) ’
Holl is worthy of special mention. He divides the levator
aiii into the ilio-coccygeus, pubo-coccygeus, and pubo-rectalis,
the same as Harrison has done. H e had previously suggested
that the name, levator ani, be discontinued. A summary of
his findings is given below.
Zlio-coccygeus. This muscle is found well developed in
many mammals, but often in man reduced to fibrous tissue.
It runs backward to gain insertion into the raphh between tlie
anus and the coccyx. I find that this muscle is the coccygeus
as described by Henle and that it is the iliac portion of the
levator of Kohlman.
Pztbo-coccggeus. This consists of two layers, superior and
inferior. The inferior layer arises from tlie entire surface of
the deep layer of the urogenital trigone and from the internal surface of the descending ramus of the pubis and the
neighboring part of the obturator fascia. The superior layer
forms a sort of gutter, opened externally and posteriorly, in
which the inferior layer is received, and it is attached to the
tip of the coccyx. The inferior layer becomes fibro-elastic
and becomes attached to the fibers of insertion of the pubococcygeus. A deep layer of the superior layer surrounds the
190
WILBUR C. SMITH
intestine like a strap. The most internal fibers of this layer
pass i n different directions to gain their insertion. Some descend to the central point of the perineum and go to form a
large p a r t of the superficial perineal muscle, or a r e continued
into the external sphincter, almost invariably some of the
fibers which remain on the same side going into the external
sphincter. Other fibers pass around the posterior border of
the urogenital diaphragm to terminate in the bulbo-cavernosus, or become attached to the inferior layer of the urogenital diaphragm. Still others find their way to the anterior
and the levator surface of the rectum, become tendinous and,
together with the smooth longitudinal fibers, find their way to
the skin of the perineum in the neighborhood of the anus, or
terminate in the central point of the perineum.
Pubo-rectalis. This arises from the posterior surface of
the body of the pubis, along a line which extends from the
inferior border of the synchondrosis toward the obturator
canal, and, further from the obturator fascia, follows a line
toward the ischial spine to the fibers of the ilio-coccygeus.
From this point of origin the fibers are directed backward in
two layers, an internal and a n external. The external layer
arises from the obturator fascia. The two layers together
pass f o r the most part behind the rectum, forming with the
fibers of the opposite side a layer which is muscular in front
and tendinous behind, and dorsally extend by means of slips
to the last sacral and the first coccygeal vertebra. It is between these two prolongations that the middle sacral artery
passes. The fibers passing beliind the rectum have no connection with its wall. Some of the fibers coming from the
back of the pubis pass in front of the rectum, some to the sides
and others posteriorly. I n front and on the sides of the rectum the connective tissue unites the latter to the pubo-coccygeus muscle, this fibro-elastic tissue emerges from the connective tissue of the pubo-coccygeus muscle itself. Some of
this fibro-elastic tissue spreads out between the fasciculi of
the external sphincter and finally terminates in the integument
of the perineum with the longitudinal fasciculi of the rectum.
THE LEVATOR AN1 MUSCLE
191
I find that this pubo-rectalis of Holl is the levator of Henle
and the pubic portions of the levator of Lartschneider, and
that also Holl describes as the pubo-coccygeus that part of the
origin of the muscle which, according to other authors, makes
up the pubo-rectalis, and vice versa.
From our modern text-books i n gross anatomy the following accounts may be mentioned: The original Gray describes
the levator ani as one muscle, but divides the fibers of insertion into three different sets, namely, the anterior, the middle,
and the posterior, as has been done by Studdiford, Sappey,
Kahbrausch, Luschka, Lesshaft, and Meriel. This description has been accepted in toto by Spitzka, Howden, and Lewis,
and Quain and Gerrish divide them similarly. Piersol and
Cunningham make no divisions of the levator, bat describe it
a s a single muscle. Bardeen, in Morris’ Anatomy, divides the
levator ani into three sets of fibers as found in the lower
vertebrates, the pubo-coccygeus, the ilio-coccygeus, and the
pubo-rectalis, but lie labels the pubo-rectalis as the pubococcygeus in his diagram. Fr o m the above mass of literature
one can readily see the problem that confronts us. There is
no single muscle in the entire human anatomy which has as
much significance to the surgeon, the gynecologist, the obstetrician, or the general practitioner as the levator ani; certainly none whose attachments and functions should be better
understood. A great deal of the literature has been contributed by these men. I include the practitioner for the
simple reason that it is he who is usually present when partial
impairment of function occurs. I t is he who so often innocently and ignorantly attempts to make repair by bringing
togclther whatever tissue may lie in front of his needle in
such a way as to get the apposition and union of the skin, but
who so often fails entirely to close the rupture of tlie fibers
of the muscle whicli is the real injury, leaving their torn ends
to retract and the interval between to become a weakening
point of the pelvic floor. Not only is tlie practitioner guilty
of this offense, but also is that surgeon who undertakes the
THI
hhATO\lIChl
KI CORI), \ 0 1 . 2 6 , 50. 3
192
WILBTTR C . SMITH
repair from surgical knowledge only, without a sufficient conception of the insertion of the various fibers or the function of
the muscle itself. I believe that in every case of confinement,
without exception, the function of the levator ani is impaired
Fig. 1 Showing perineum of a girl of about twelve years of age, viewed
from below. All of the superficial muscles, with the exception of the external
sphincter ani, have been removed. The lerator a n i muscle from this view shows
principally the pubo-rectalis and the ilio-coccygeus. The former can be seen as a
thick band of fibers, thc most mesial of which surround the vagina, forming its
true sphincter. The fibers behind the pubo-rectalis constitute the ilio-coccygeus.
The most posterior muscle in the space is the coccygeus, represented by a small
but distinct bundle of fibers. The vagina and the anus a r e seen t o be opening
at right angles t o each other. It is t o b e noted especially t h a t the anus is directed almost straight backward.
T H E LEVATOR AN1 MUSCLE
193
to a greater or less extent by stretching or tearing some of its
fibers. Often the fibers a r e ruptured, though the skin and
mucous membrane remain intact. I have always tried to impart to the student that the rupturing of a muscle o r any part
of its fibers results quite similarly to the retraction of rubber
after rupture when placed on tension.
Fig. 2 Shows the levator a n i muscle from above, adult male. The most
anterior and medial fibers, which a r e on a lower plane, belong t o the pubo-rect a l k The most prominent muscle, the pubo-coccygeus, which resembles a V and
embraces the anus, extends back to the t i p of the coccyx. Lateral t o this and
lying in a lower plane, t h e ilio-coeeygeal fasciculi a r e disposed at a n obtuse angle
with the former. The coccygeus occupies the remainder of the pelvic floor.
194
WILBUR C . SMITH
One finds it refreshing to read the descriptions of this
muscle in the scientific publications of Savage, Thompson,
Hogge, Hart, Lartschneider, and Holl, authors who have
equal knowledge in human and comparative anatomy, but it
seems curious to note that in all the literature to which I have
had access (save perhaps the atlas of Hart) not a single illustration shows the openings of the perineum in tlieir correct
anatomical position. This lack is especially true for tlie anus.
Tlie anal opening, according to my own observations, points
hack at an angle of nearly 80". Many authors have stated
that tlic vagina and the anus lie at riglit angles to one another, which is quite true, but they make no reference as to
horn tlie openings point. Their diagrams sliow tlie openings
of tlie anus pointing almost straight down in the standing POsition, o r sometimes back a t an angle of about 15". I believe
H a r t recognized the correct condition, but, as is stated by
inany others, he shows the anal opening back toward tlie point
of the coccyx, necessarily omitting the levator ani muscle between the two. While practically all authors, with a few
exceptions, agree as to the general origin o f tlie levator ani,
it is its insertion and its function which have given rise to so
much confusion in descriptions and controversy.
I have found (figs. 1 to 4) that in both tlie male and feinalc,
by careful dissection of many subjects, tlie levator ani is composed of three distinct sets or fibers, both at its origin and at
its insertion, namely, tlie pubo-coccygeus, ilio-coccygeus anti
the pubo-rectalis, as described by Bardeen.
The pubo-coccygeus, best seen from above (fig. 2 ) , springs
from the pclvic surface o f the body of the pubis and the superior mmi, back as far as the attacliment of the ilio-coccyg ~ u s . It is a thin, strap-like muscle, ~vliicli rests upon tlie
npper surface of the pubo-rrctalis and tlie ilio-coccygeus.
From their origin its buntlles pass bacliward and medialmard,
a few fibers from tlie medial border passing in front of the
rectum (fig. 2 ) to blend with tliose of tlie opposite side and
m-itli tlie sphincter ani. Lateral t o these, a band of ahout 1%
THE LEVATOR A N 1 MUSCLE
195
em. in breadth surrounds the rectum like a collar. The major
portion of the muscle extends backward, uniting with its fellow across the mid-line between the anus and the coccyx, but
some fibers continue backwards to become attached to the
lower three or four coccygeal vertebrae.
Fig. 3 Inferior vicw of the perineum of a nullipara in which all the superficial iiiuscles have been removed with the exception of the external sphincter ani.
S1ioi.c.s the openings of the vagina and anus, the fibers of the pubo-rectalis, iliococcygeus, and coccygeus muscles. Compare with figure 1, noting particularly
clifferences in laxity and direction of levator fasciculi. The conditions exhibited
may be attributed to mechanical factors other than gestation and labor-intercourse, for example.
1'36
WILBUR C. SMITH
The ilio-coccygeus (figs. I to 4 ) , the broadest, thinnest, and
the most degenerated division of the levator ani, takes its
origin from the pelvic surface of the ischial spine and from
the arcuate line, o r white line. This line consists of fascia
extending obliquely upward a s f a r as the superior ramus of
the pubis, in the region of the obturator canal. F r o m this
latter origin, its bundles run almost transversely medialward,
most of them joining the opposite fellow between the anus and
coccyx. Some, by means of a n aponeurosis, become attached
to tlie lower coccygeal vertebrae.
The pubo-rectalis, tlie most massive p a r t of the levator m i ,
takes its origin from the lateral edge of the pelvic surface of
tlie body of the pubis, from the pelvic surface of the proximal
p a r t of the descending pubic rami, and from tlie upper layer
of the urogenital trigone. The fibers pass almost directly
backward, close to tlie side of the vagina, to gain their insertions. Upon reaching the posterior part of the vagina, a band
departs from the medial margin of the muscle. The terrnination of this band is traceable to its fellow of tlie opposite side
and to the opposite external sphincter ani. Froin the lattor
termination, a few fibers may be further distinguished, being
attached by means of elastic tissue into tlie neighboring skin.
The bulk of the muscle passes still farther backward along
the lateral surface of the external sphincter ani to fuse with
the corresponding opposite muscle between the anus and tlie
coccyx, but a small contribution continues from it to the
coccyx, either as muscle fibers o r aponeurosis (fig 4). On
passing along tlie lateral side of the sphincter ani, some of the
fibers become lost in the fibers of the sphincter itself, and
some of then1 terminate in elastic tissue, which ends in the
skin around the anus. The proportion of fibers running to
the skin amount to very little. However, fibers from both
this arid the pubo-coccygeus, as noted above, terminate in the
skin.
I must agree with most of the authors stating that no fibers
of the levator terminate in the rectal or vaginal walls proper.
T H E LEVATOR A R I MUSCLE
197
Furthermore, T am convinced that tlie pubo-rectalis is tlie true
vaginal sphincter.
Aware of the difficulty in obtaining a nullipara in tlie dissecting room, I have often been concerned with the question
of whetlier the descriptions of the levator ani muscle have not
orignated from subjects like that illustrated in figure 5, a
multipara. Doubtless some descriptions deal with multiparae
Fig. 4 Lateral aspect of the levator ani, adult male. The fasciculi of the
pubo-rectalis and ilio-coecygeus can be traced from origin to insertion.
198
WILBUR C . S M I T H
in wliich tlie skin and mucous membrane had never been torn,
o r possibly subjects in which repair had been made sometimi.
prior to death. These, to the naked eye, could easily be mistaken f o r normal perinea. Such material might account for
the variations in tlie numerous descriptions of this muscle,
especially a s regards the insertion of its fibers. I have included a drawing from such a multipara (fig. 5) to illustrate
this possible explanation of these variations.
Dissections of the various perinea of parous women often
suggest that the fibers of the right levator may differ somewhat from those of the left. The arching of the levator fibers
often appear more pronounced in parous females than in
iiulliprae. On the right side they may form a wider curve
than on the left. This may be accounted for from tlie fact that
in 90 per cent of all cases of labor there is either a LOA or n
ROP position of the Iiclacl. This means that the posterior
aspect of the head of the child must come to press upon tlie
right side of the pelvic floor. l’lic right side of the muscle
mill naturally become more stretched and is more liable to tear
tliaii the left side.
My experience with tlie levator ani lias taught me that
even in the nullipara there occurs a certain amount of variation of its fibers. I n some subjects the fibers passing beliincl
the vagina seem t o comprise a rather large bundle and in
others they seem greatly reduced. I n some specimens tliere
appears to be a greater proportion of fibers termiiiatiiig in
elastic tissue which runs to tlie skin tlian in others. I n sonic
cases one finds muscular fibers continuing back to the coccyx
and in others they appear to terminate in an aponeurosis
wliicli gains its attachments to the coccyx. Tlie ilio-coccygeus
seldom appears the same in any two subjects. I n some it is
fairly well developed and in others quite thin and aponeurotic.
This latter condition is invariably found in old subjects o r in
those in which laceration has occurred, and it is responsible,
no doubt, f o r impaired functions of the pelvic diapliragm.
Fig. .5 Lateral view of the levator a n i of R parous female, sliowing a laceration e\tending to anterior margin of anal opening, including fillers of botli
levator a n i and external sphincter ani. The origin of the fibers of both the puborertalis and the ilio-coccygens a r e distinctly indicated, the former terminating
bluntly in the side of the vagina-a
condition which is caused by ruptures of the
fibers hetveen anus land vagina and by subsequent retraction of the most mesial
portion of the muscle to its present position. A considerable mass of cicatrical
tissue 'iws present between the torn ends of this portion and the vaginal wall
a n d in the interval between tlie torn edges of the group between anus a n d
vagina. The ilio-coccygeus appears to be normal in its attachments, but is very
thin and seems somewhat more degenerated than is usually found. The eoccggeus
is the most dorsal muscle in the space. It is considerahly atrophied a n d
most of its fibers terminate by a n apoiieurosis vlhicli extends backward t o tlie
COCCyY.
190
200
WILBUR C . SNITH
I n about 30 per cent of tlie bodies, inale and female, personally examined, a p a r t of the levator ani lies superficially
to the posterior margin of the urogenital diaphragm. This
part of the muscle is described when present as tlie superficial
transverse peroneal.
Almost every conceivable function has been attributetl to
the levator ani muscle. I cannot agree with all the functions
advanced. I do not think that this muscle has any perceptible
function upon the coccyx, even though the opinion that it does
is almost unanimous. While a considerable number of its
fibers a r e inserted to tlie coccyx, it must be kept in mind that
the coccyx has but very little movement in the joint between
itself and the sacrum. Normally this is an ossified joint. It is,
however, the principal, or the true spliiricter of the vagina. It
acts also as a partial sphincter to tlie rectum in forcing out
the contents of its lower end. It is the most essential single
structure of the pelvic diaphragm ; its most important function being, as pointed out by Paramore, to resist intra-ab(1ominal pressure.
SUMMARY
I t is advanced that the pubo-rectalis muscle, a division of
the levator ani, forms the real sphincter of the vagina; that
the lumen of tlie anus is directed backward at an angle of
about 80" with the long axis of the body instead of parallel
with this axis, as many have pictured it; that the superficial
transverse perinei muscles, when present, are fasciculi of tlie
levator ani, and that iiiuch of the confusion concerning the
levator ani is due to descriptions of it in inultiparous subjects
claimed to have been nulliparous.
THE LEVATOR AN1 MUSCLE
"01
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~ 1 0 ~
d
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