BMJ 1999;319:1596-1600
( 18 December )
Papers
Magnetic resonance imaging of male and female genitals during coitus and
female sexual arousal
Willibrord Weijmar Schultz, associate
professor of gynaecology a, Pek van
Andel, physiologist b,
Ida Sabelis, anthropologist
d, Eduard Mooyaart,
radiologist c.
a Department of Gynaecology, University Hospital Groningen,
PO Box 30 001, 9700 RB Groningen, Netherlands,
b Laboratory for Cell Biology and Electron Microscopy,
University Hospital Groningen, c Department of Radiology,
University Hospital Groningen, d Department of Business
Anthropology VU, De Boelen 1081C-NL, 1081 HV, Amsterdam
Correspondence to: W Weijmar Schultz w.c.m.weymar.schultz@oprit.rug.nl
 |
Abstract |
Objective: To find out whether taking images of the male
and female genitals during coitus is feasible and to find out
whether former and current ideas about the anatomy during sexual
intercourse and during female sexual arousal are based on assumptions
or on facts.
Design: Observational study.
Setting: University hospital in the Netherlands.
Methods: Magnetic resonance imaging was used to study the
female sexual response and the male and female genitals during
coitus. Thirteen experiments were performed with eight couples
and three single women.
Results: The images obtained
showed that during intercourse in the "missionary position" the penis
has the shape of a boomerang and 1/3 of its length consists of the
root of the penis. During female sexual arousal without intercourse
the uterus was raised and the anterior vaginal wall lengthened. The
size of the uterus did not increase during sexual arousal.
Conclusion: Taking magnetic resonance images of the male
and female genitals during coitus is feasible and contributes
to understanding of anatomy.
| |
Introduction |
"I expose to men the origin of their first, and perhaps second, reason for
existing."1
Leonardo da Vinci (1452-1519) wrote these words above his drawing
"The Copulation" in about 1493 (fig 1).2 The
Renaissance sketch shows a transparent view of the anatomy of sexual
intercourse as envisaged by the anatomists of his time. The semen was
supposed to come down from the brain through a channel which can be
seen in the spine of the man. In the woman the right lactiferous duct
is depicted as originating in the right female breast and ending in
the genital area. Even a genius like Leonardo da Vinci distorted
men's and women's bodies
as seen nowto fit the ideology of
his time and to the notions of his colleagues, who he paid tribute
to.
|
Fig 1. "The Copulation" as
imagined and drawn by Leonardo da Vinci.2 With permission
from the Royal Collection. Her Majesty Queen Elizabeth II is
gratefully acknowledged
| |
The first careful studysince the sketch by Leonardo da Vinciof the
interaction of male and female human genitals during coitus was
published by Dickinson in 1933 (fig 2).3 A
glass test tube as big as a penis in erection inserted into the
vagina of female subjects who were sexually aroused by clitoral
stimulation (occasionally with a vibrator) guided him in constructing
his pictorial supposition.
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Fig 2. Midsagittal image of
the anatomy of sexual intercourse envisaged by R L Dickinson and
drawn by R S Kendall3
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In the 1960s Masters and Johnson made their assessments with an artificial
penis that could mechanically imitate natural coitus and by "direct
observation"the introduction of a speculum and
bimanual palpation. 4 5
Their most remarkable observations regarding sexual arousal in the
woman were the backwards and upwards movements of the anterior
vaginal wall (vaginal tenting) and a 50-100% greater volume of the
uterus. This increase disappeared 10-20 minutes after orgasm.
When sexual excitement without orgasm occurred, the volume returned
to normal in 30-60 minutes. Masters and Johnson presumed that
the greater volume of the uterus was due to engorgement with blood.
However, they qualified their presumption: "In view of the artificial
nature of the equipment, legitimate issue may be raised with the
integrity of observed reaction patterns."4
In 1992 Riley et al published an ultrasound study on copulation.6 The
images were of relatively poor quality as they used hand held, self
scanning equipment, and none of the images was overview. We used
magnetic resonance imaging to study the anatomy and physiology of
human sexual intercourse. Our search started in 1991 when one of
us (PvA) saw a black and white slide of a midsagittal magnetic
resonance image of the mouth and throat of a professional singer who
was singing "aaa." He remembered Leonardo's drawing and wondered
whether it would be possible to take such an image of human coitus.
We decided to try, as an ad hoc "instrument-oriented" study, despite
the unscientific and other irrelevant reactions we expected and
received: honi soit, qui mal y pense.
Magnetic resonance imaging had already been used as a diagnostic tool to
study erectile impotence7; it
is particularly attractive for this kind of study because it produces
images with exquisite anatomical detail that are clearer than those
obtained with ultrasonography or radiography, andas far as we knowit
is safe. The aim of the study was initially to find out whether
taking images of the male and female genitals during coitus is
feasible, and later whether former and current ideas about the
anatomy during sexual intercourse and during female sexual arousal
are based on assumptions or on facts.
| |
Subjects and methods |
The participants (pairs of men and women) were recruited by personal
invitation and through a local scientific television programme.
Respondents were invited to participate if they met the following
criteria: older than 18 years, intact uterus and ovaries, and a
small to average weight/height index. The experimental procedure was
explained in a letter sent to respondents along with an informed
consent form. Participants were assured confidentiality, privacy,
anonymity, and the possibility of withdrawing from the study at any
time. After written informed consent had been obtained, the
participants were invited to come for a scan when the equipment was
available on a Saturday.
The tube in which the couple would have intercourse stood in a room next to a
control room where the searchers were sitting behind the scanning
console and screen. An improvised curtain covered the window between
the two rooms, so the intercom was the only means of communication.
Imaging was first done in a 1.5 Tesla Philips magnet system
(Gyroscan S15) and later in a 1.5 Tesla magnet system from
Siemens Vision. To increase the space in the tube, the table was
removed: the internal diameter of the tube is then 50 cm. The
participants were asked to lie with pelvises near the marked centre
of the tube and not to move during imaging. After a preview,
10 mm thick sagittal images were taken with a half-Fourier
acquisition single shot turbo SE T2 weighted pulse sequence (HASTE).
The echo time was 64 ms, with a repetition time of 4.4 ms.
With this fast acquisition technique, 11 slices of relatively
good quality were obtained within 14 seconds.
The volunteers were shown the equipment in the two rooms, and personal and
gynaecological histories were taken. The experimental procedure was
explained, and all investigators left the imaging room. After a
preliminary image for positioning the true pelvis of the woman was
taken, the first image was taken with her lying on her back (image
1). Then the male was asked to climb into the tube and begin face to
face coitus in the superior position (image 2). After this shotsuccessful
or notthe man was asked to leave the
tube and the woman was asked to stimulate her clitoris manually and
to inform the researchers by intercom when she had reached the
preorgasmic stage. Then she stopped the autostimulation for a third
image (image 3). After that image was taken the woman restarted the
stimulation to achieve an orgasm. Twenty minutes after the orgasm,
the fourth image was taken (image 4). At the end of the experiment,
the images were evaluated in the presence of the
participants.
| |
Results |
Thirteen experiments were performed with eight couples (three couples
performed two experiments each) and three single women. The table
shows age, weight/height index, parity, type of contraception, female
orgasm (yes/no), and the depth of penetration (partial or complete).
No women reported having a "g-spot" or producing female ejaculation
during orgasm. On two Saturdays in 1991 (experiments 1 and
2) the first couple succeeded with complete penetration that lasted
sufficiently long for the images to be taken. The Philips
1.5 Tesla magnet system at that time required a relatively long
acquisition time (52 seconds) and had a relatively poor signal:noise
ratio. This gave low quality images with many movement artefacts.
In 1996 the Siemens Vision 1.5 Tesla magnet system became
available and provided the opportunity to continue our search for
sharp images. Six couples succeeded in partial, though not
complete, penetration (experiments 3 and 7-11). In
1998 sildenafil (Viagra) became available in the Netherlands.
The two couples in experiments 9 and 11 were invited to
repeat the procedure one hour after the man had taken one 25 mg
tablet of sildenafil. They succeeded with complete penetration that
lasted long enough (12 seconds) for sharp images to be taken
(experiments 12 and 13).
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Fig 3. Midsagittal image of
the anatomy of sexual intercourse (experiment 12). P=penis,
Ur=urethra, Pe=perineum, U=uterus, S=symphysis, B=bladder,
I=intestine, L5=lumbar 5, Sc=scrotum
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Fig 4. Midsagittal images of
sexual response in a multiparous woman (experiment 9): (left) at
rest; (centre) pre-orgasmic phase; (right) 20 minutes after
orgasm
| |
Figure 3
shows a midsagittal image of the anatomy of sexual intercourse with the woman
lying on her back and the man on top of her. The root of the penis
(1/3 of the length) and the erect pendulous body (2/3 of the length)
are visible. The pendulous part of the erect penis moved upwards at
an angle of about 120° to the root of the penis, and almost parallel
to the woman's spine. In all the experiments this phenomenon occurred
in this coital position and was not related to the depth of
penetration. In complete penetration the penis filled up the anterior
fornix (experiments 1, 2, and 13) or the posterior fornix
(experiment 12; fig 3).
During intromission the pubic bones of the men and the women did
not approach each other closely: the female pubic bone stayed
about 4 cm cranial to that of the male. The uterus was raised
by 2.4 cm. The changed configuration of the bladder was caused
by penile stretching of the anterior vaginal wall during
intromission, plus the raising of the uterus and the increase in
bladder size as it filled. The subjective level of sexual arousal of
the participants, men and women, during the experiment was described
afterwards as average.
Eight women had a complete sexual response during sexual stimulation
(experiments 4-11) and these women described their orgasm as
"superficial." The sexual response of one of these women is shown in
figure 4. In
the pre-orgasmic phase the anterior vaginal wall lengthened by
1 cm and the uterus rose within the pelvis. This is a typical
response in all experiments except one (experiment 10). During sexual
arousal without coitus, the position and size of the uterus hardly
changed. It was not possible on these magnetic resonance images to
distinguish between the vaginal wall, the urethra, and the clitoris.
These images did not show widening of the vaginal canal, structures
suggesting a Gräfenberg spot, or a separate reservoir of fluid
indicating "female ejaculation."
| |
Discussion |
In Sex and the Human Female Reproductive Tract Levin stated: "The
scientific study of the interaction of human genitals during coitus
and after ejaculation with and without female orgasm has always been
difficult and controversial with ethical, technical and social
problems."8 We
experienced this personally. It took years, a lobby, undesired
publicity, and a godsend (two tablets of sildenafil 25 mg) to
obtain our images. They show that such pictures are feasible and add
to our knowledge of anatomy.9
We did not foresee that the men would have more problems with sexual
performance (maintaining their erection) than the women in the
scanner. All the women had a complete sexual response, but they
described their orgasm as superficial. Only the first couple was able
to perform coitus adequately without sildenafil (experiments
1 and 2). The reason might be that they were the only
participants in the real sense: involved in the research right from
the beginning because of their scientific curiosity, knowledge of the
body, and artistic commitment. And as amateur street acrobats they
are trained and used to performing under stress.
Anatomy revealed
The hypothesised anatomy of human
coitus, as drawn by Leonardo da Vinci in about 1493 and by
Dickinson in 1933, could be tested with magnetic resonance
imaging. According to our images, the caudal position of the male
pelvis during intercourse, the potential size of the bulb of the
corpus spongiosum, and the capacity of the penis in erection to make
an angle of around 120° to the root of the penis, enabled penetration
along the bottom of the symphysis up to the woman's promontorium (fig
3) or to
the middle part of the sacrum (fig 4) almost
parallel to her spine. The "hidden" position of the root of the penis
must have been the reason for the difference between the angle of
penetration as envisaged by Dickinson and the penetration angle on
our images. The images showed that during "missionary position"
intercourse the penis is not straight, as drawn by Leonardo. It has
the shape of a boomerang and not of an S as envisaged by Dickinson.
Leonardo and Dickinson clearly underestimated the size of the root of
the penis. Scanning of the position of the human genitals during
coitus gives a convincing impression of the enormous size of the
average penis in erection (root plus pendulous part is 22 cm)
and of the volume of vaginal and pelvic space required by the
pendulous part of the penis.
Contemporary scientific
knowledge about internal genital changes during female sexual arousal relates
mainly to the vagina (thickening of the vaginal wall due to
vasodilation, lubrication, widening of the vaginal cavity), the
urethra (possible engorgement of the vascular tissue of the urethra),
and the uterus (upwards movement of the uterus=tenting effect+change
in position of the uterus+change in size of the uterus). Recent
research on the anatomical relation between urethra and clitoris
showed that the perineal urethra is embedded in the anterior vaginal
wall and is surrounded by erectile tissue in all directions except
posteriorly where it relates to the vaginal wall.10
The bulbs of the vestibule directly relate to the other clitoral
components and the urethra. Details of the vaginal wall, the urethra,
and the bulbs of the vestibule were unfortunately beyond the
resolution of our current equipment. However, we were able to see
displacement of the uterus (upwards) and lengthening of the anterior
vaginal wall and hardly any change in the position of the uterus
during sexual arousal, unless it was caused by intromission of
the penis.
In contrast to the findings of Masters and Johnson,4 our
images did not show an increase in the size of the uterus during
sexual arousal. These observations are not surprising. From an
anatomical and physiological point of view there is no basis for
a 50-100% increase in the volume of the uterus in such a short
time. Masters and Johnson made their observations with bimanual
palpation. Their interpretation may have been caused by the raising
of the uterus or filling of the bladder during their
experiments.
Changes during sexual arousal
Magnetic resonance
imaging showed strikingly that during female sexual arousal changes
occurred in the anterior vaginal wall. These changes took place in
the vaginal wall itself (the engorgement as such is not visible on
the images), through the raising of the uterus, displacement of the
uterus caused by penetration of the penis, and through gradual
filling of the bladder. Histological studies 11
12
and immunohistochemistry13
have shown that the anterior wall of the vagina has denser
innervation than the posterior wall. This is supported by clinical
studies 14
15
and research into vaginal sensitivity to electric stimuli16
in which the anterior vaginal wallwith the urethra behind itwas
found to be relatively sensitive. Hoch's concept of a
clitoral-vaginal sensory arm of the orgasmic reflex refers
specifically to the anterior vaginal wall and the deeper tissuesthe
urinary bladder, the periurethral tissues, and Halban's fascia15and our
images support this.
Conclusion
What started as artistic and scientific
curiosity has now been realised. We have shown that magnetic
resonance images of the female sexual response and the male and
female genitals during coitus are feasible and beautiful; that the
penis during intercourse in the "missionary position" has the shape
of a boomerang and not of an S as drawn by Dickinson; and that, in
contrast to the findings of Masters and Johnson, there was no
evidence of an increase in the volume of the uterus during sexual
arousal.
| What is already known on
this topic
It has been extremely difficult to investigate anatomical changes
during the act of coitus and the female sexual response
Modern magnetic resonance imaging allows exploration of aspects of
living anatomy What this paper
adds
Taking MR images of the male and female genitals during coitus is
feasible
During `missionary position' intercourse the penis has the shape of a
boomerang
During female sexual arousal without intercourse the uterus rises and
the anterior vaginal wall lengthens
The size of the uterus does not increase during sexual arousal
|
The Polish-German physician and philosopher Ludwik Fleck (1896-1961) used
images of female genital anatomy to illustrate the cultural
conditioning of scientific knowledge. In his treatise Genesis and
Development of a Scientific Fact he states: "In science, just as
in art and in life, only what is true to culture is true to
nature."17
Magnetic resonance images, objective as they are, show the anatomy of
human coitus and the female sexual response that is true to
nature.
| |
Acknowledgments |
We thank our volunteers for their cooperation, laughter, and permission to
publish intimate MR images of them; those hospital officials on duty
who had the intellectual courage to allow us to continue this search
despite obtrusive and sniffing press hounds; Professor J Kremer for
his encouragement to use the scanner to study female sexology and for
his critical reading the typescript; and Professor W Mali for
offering the use of equipment at the University Hospital Utrecht. P
van Andel does not want to be acknowledged for his idea of using MRI
to study coitus. He excuses himself by quoting the French romantic
poet Alphonse de Lamartine (1790-1869): "C'est singulier! Moi, je
pense jamais, mes idées pensent pour moi."
Contributors: WWS initiated and coordinated the formulation of the study
hypothesis, designed the protocol, and participated in data collection,
interpretation of the findings, and writing of the paper; he is guarantor of the
study. PvA had the original idea for the present study, and participated in
formulation of the study hypothesis, data collection, interpretation of the
findings, and writing of the paper. IS, together with her partner, participated
in the first two experiments and helped design the protocol. EM participated in
the execution of the study, particularly data collection and interpretation of
the magnetic resonance findings.
| |
Footnotes |
Funding: No additional funding.
Competing interests: None declared.
| |
References |
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Abstract 
Introduction 