article should be read in conjunction with the article on Average
I apologise for the unavoidable plethora of medical names.]
One of the
distinctions between a genetic man and a genetic woman is the
characteristics of their skeleton. The skeleton obviously sets
or heavily influences the body size and its
and Jessica (right) are
very beautiful transsexual woman. But a close inspection of their
build reveals male
It's thought that
genes (usually female "XX" or male "XY") mainly
determine the basic size and shape of the skeleton, however some
differences are exaggerated or emphasised at puberty by the sex hormones
that surge around the growing body. The high levels of testosterone that appear in boys at
puberty help lengthen and rugged'ise their still developing bones,
enhancing and developing male skeletal characteristics such greater height
and narrower pelvic width. The near absence in girls of these
hormones prevents such skeletal developments; indeed the presence of high
levels of oestrogen in a pubertal girl probably helps stimulate the growth
and shape of her pelvic bones, but otherwise actually act to limit bone growth and
final adult height.
[Appropriate hormonal treatment in a young transsexual
can thus have substantial benefits in terms of skeletal development,
benefits not obtainable after puberty when bone development is essentially
Despite the sex
related differences, overall the differences between the skeletons of male
and female bodies are actually surprisingly small compared with the
similarities, as is illustrated by comparing the following diagrams:
baby's skeleton has 350 bones, but many of these fuse to give an
adult a total of 206 bones. A
man's skeleton has broader shoulders than a
woman's, a longer
ribcage, and a pelvic girdle optimised for walking/running.
woman's skeleton has the same bone complement as
a man's but is slightly smaller and less robust, with a wider pelvic opening
to assist childbirth.
Born a boy, former Las Vegas showgirl
Jahna Steele had
the small and slight skeletal build
common in women but very rare in men.
Skeletal Sex Differentiation
It is actually
quite difficult to distinguish between male and female skeletons as there
is a clear range of overlap between the sexes for many measures.
Indeed, there is in fact no certain, 100% guaranteed, method of telling
the sex of a skeleton from simple examination and inspection alone, as
criminologists who have misidentified the sex of murder victims, and
archaeologists who have been unable to determine from skeleton X-Rays
whether Egyptian Pharaoh Tutankhamen was actually male or female, can
On average a male
skeleton is larger than the female skeleton so this is a differentiation,
but there is also a considerable overlap in skeletal size between the
sexes - e.g. there are short men and tall women - so this is hardly
a reliable method alone. Other significant differences between
male and female skeletons are that female bones are usually lighter and
thinner than more robust male bones; female head bones are smaller and
more lightly built; and the female pelvis is shallower and wider than the
male's. This latter difference makes childbirth
easier. The pelvis is considered to be the best area to determine
or estimate the
sex of a skeleton, while the skull (cranium and mandible) and postcranial
skeleton is the second best area.
weight and height have little overlap between male and female
skeletons, and thus can distinguish between men and women with a 90%
success rate. Transsexual women would generally be
identified as men on these criteria. (Sample sets of 125 men and 138
women are illustrated)
Skull and bone
features vary from male to female - differentiation is usually based on
the generalization that "typical male" features are more pronounced and
marked than the same features in a female. By observing all
the possible differentiating features of skeleton in a cumulative manner,
it's possible to correctly identify the sex of a Caucasoid skeleton in
about 90% of cases. [Krogman ranks accuracy of sex determination using the
pelvis at 95%, followed by the skull at 92%, the mandible alone at 90%,
and long bone measures at 80%. Stewart indicates slightly
lower yields, however the order of accuracy was the same, with the long
bones again the least accurate.] Success rates are somewhat lower
for Negroid and Mongoloid skeletons.
The physical similarity
of "super models" such as Gisele Bundchen (left) to transsexuals such
as Caroline Cossey has caused
speculation and highlights the overlap in human sexual differentiation.
Note that it is
often impossible to place absolute metric value on what constitutes a male
feature, and what constitutes a female. Krogman addressed the
difficulty of sex determination from skeletons when he stated: "here
is the problem of subjectivity versus objectivity, of description versus
measurement, of ‘experience’ versus statistical ‘standardization.’ "
Transsexual actress Claudia Cherriez.
An extraordinarily beautiful woman with male skeletal characteristics
- most notably in this image the length of her limbs and the shape
of her jaw bone; her breast implants are
also very obvious.
female skull retains gracile attributes seen in the pre-pubescent skull,
but the male cranium becomes markedly rougher in adulthood at the sites of
differences between the female and male skill include the
posterior of the cranium (the occipital), robusticity of the
browridge, mastoid process, nuchal crest, temporal lines, and
mandible. Although distinct, the ability to quantify
measures of the skull for sex determination has met with limited
success and successful sex identification based purely on a skull
is a very subjective process based experience in identifying and
assessing non-metric characteristics.
male and female faces. Notice the man's square face,
heavy brow, prow nose, bigger jaw, and the woman's lighter build,
triangular shape, high vertical forehead, no browridges, small
nose, pointed chin.
the orbits (eye sockets), the male cranium tends to have "blunt"
superior margins and larger supraorbital (brow) ridges. The female
cranium tends to have "sharp" superior margins of the orbits and
no discernable supraorbital ridges.
occipital of males tend to have a well-defined nuchal crest. In some
cases, the nuchal crest and nuchal line are very rugged and sharp.
In very gracile females, there is almost no nuchal crest and the nuchal
line is completely absent.
mandible of a female cranium tends to have a "pointed"
chin. The area around the gonial angle is smooth and does not
project. The male mandible tends to have a "square" shape
and in extreme case the area around the gonial angle is
"flared". The dentition (teeth) of males is frequently
the area of the temporal in the female cranium is smoother and less rugged
than that of the male cranium. In the female cranium the zygomatic
arch normally does not extend, as a ridge, posterior of the external
auditory meatus. In male crania the zygomatic arch typically
extends, as a ridge, posterior to the external auditory meatus. In
females the mastoid process is small and smooth. In males the
mastoid process is large and rugged.
Female Cranium Differences
important skull differences between men and women are indicated by
the letter value on the figure to the left and described below:
The mans cranial mass is more blocky and massive compared to the
females which is rounder and tapers at the top.
B) Temporal Ridge - runs along the outer side of the upper skull
creating the square shaped of the upper head. More prominent in
men than women.
C) A woman's supraorbital margin (the ridge above the eyes) is
sharper, while the males is rather round and dull.
D) The Zygomatic bone (the cheekbone that lies under the lower eye
ridge) is more pronounced on the male skull.
E) The Mandible (lower jaw) bone of a woman is rounded, while
the male's is squared.
F) Frontal bone – forehead structure terminates at the brow. The
male forehead is lower and more slopping.
G) Men have a deeper cranial mass.
H) The supercilary arch is large and pronounced in the man.
I) A males gonion (most posterior inferior point on angle of
mandible) is more flared out and sharply angled.
J) The teeth of men tend to be larger.
Here is a summary
of the differential criteria between the male and female cranium bones:
vertical and rounded
superciliary arches (browridges)
process (bone behind the ear)
margin (ridge above eye)
occipital protuberance (protrusion on lower back of the cranium)
crest (low ridge along the back base of the cranium)
process (cheek bones)
and more robust
and mental eminence of mandible (chin)
of mandible (back of jaw bone)
gonion and gonion angle (back corner of jaw bone)
and sharply angled
and larger by about 10%
may vary. Exceptions occur frequently.
relating the skull differences just described to the face.
Unfortunately for the transsexual woman, the human eye and brain is
amazingly able to distinguish between a "male" face and a
"female" face on the basis of very minor differentiations and
However, as ever,
there is great variance - many handsome actors on close examination have
some feminine facial characteristics, while many supermodels have some
very male characteristics.
absolute measures almost all dimensions of the female skull and face
are smaller compared to the male features. The facial width is
relatively larger in women than in men. Resulting contours are
therefore more rounded in females, especially in the orbital area,
with more prominent malar (cheek) bones and less prominent
mandibular (chin/jaw) angles.
In the upper part of the face, the forehead is quite different, most
noticeably women have less sloping mid-foreheads and the position of
their eyebrows is higher and has a stronger curvature.
In the middle part of the face, the angles of the nose differ
substantially, especially at the tip portion. Females generally have
a more pointed, narrow, and vertically shortened less nasal prominence
In the lower part of the face the most dominant differences are
found in the chin region, which varies markedly between the male and
female. The male chin is larger in every dimension, the manible
symphysis (upper chin) is generally wide and vertically high,
while the female is more rounded, and the male mental eminence
(point of the chin) tends to be square and the female more
pointed. The degree of perceived masculinity/femininity due to
the chin can vary tremendously.
girl, but she is a XY transsexual and her skeleton -including her
pelvis - still reflects this past. Only the pre-puberty taking
hormones can materially affect the skeleton, and that is very rare
other than for intersex children.
The pelvic girdle is formed by the sacrum, coccyx, and the two
coxae. A coxa is formed by the fusion of three bones, the ilium,
ischium, and pubis, which meet in the acetabulum or hip socket. At
the back each coxa is attached by strong ligaments to the sacrum (base of
spinal cord), and in front to each other at the pubic symphysis joint.
This joint allows only slight bending movement, but it softens and becomes
more flexible in a female giving birth. [Note: Other names for the
pelvic bone are innominate bone and coxal bone.]
sex differences are true for the hypothetical "average" male and
have penises and testes; females have vaginas and wombs.
Males and females differ in form. Their curves and angles. or
their shapes are different, generally and relatively. Females
generally have a more roundish look because their subcutaneous fat
covers and hides their muscles. Men do not have women's
characteristic layers of fat beneath their skin, and therefore their
appearance is more roughish because their muscle tissues show through
their skin more so than females.
Women's eyes are set further apart than men's. Women's eye brow is
lighter than men's in appearance. Looking toward the front,
women's face is rounder, broader than men's. Looking from the
top down on the head, women's head is rounder, while men's head is
longer from front to back.
Women have developed breasts with larger nipples and areolas than
men. Women's shoulders are more narrow, rounded, and sloping
Arms and Legs
The angle of women's thigh and lower leg gives a "knock-knee"
effect to females, while men's form a straight line. Also
women's arms form a bent "carrying angle" at the elbow, while men's
"carrying angle" is straight.
Looking towards the front, women's hips are wider than men's, and
their hips have a more round'ish curve than men's. Women's legs
have a conical shape, while men's legs have a cylindrical look.
Women's hands and feet are relatively smaller, narrower, and more
delicate looking than men's.
Women do not have noticeable hair like men on their chest, arms,
legs and other bodily areas. Women's pubic hair is formed like a
triangle pointing down; men's pubic hair forms a triangle pointing up.
Women do not loose head hair like many men do in old age.
Women are generally smaller and more delicate than men. The following
apply generally for those of western European descent:
By age 20 years, women are generally 10 percent shorter than men.
By age 20, women are generally 20 percent lighter than men.
men are generally 50 to 60 percent stronger than women.
contributing to the overall shape of the pelvis are constrained by both
the demands of bipedal locomotion, as well as those for perpetuating the
species. Of all the bones, the pelvis shows the greatest
sexual differentiation, principally in relation to the requirements of
childbirth. On average the male pelvis is much heavier and narrower
than that of the female. In comparison the female pelvis is broad
and shallow, the geometry is designed with a greater outlet for passage
through its bony openings of a baby's head and shoulders during
birth. The female pelvis is also less massive and more delicate and
its muscular impressions are slightly marked.
In the female
pelvis the ilia are less sloped, and the anterior iliac spines more widely
separated; hence the greater lateral prominence of the hips. The
pelvic inlet of females is larger and has a greater absolute
circumference. The body of the pubis is longer, thereby increasing the
size of the pelvic outlet. The size of the pelvis varies not only in
the two sexes, but also in different members of the same sex, and does not
appear to be influenced in any way by the height of the individual.
Women of short stature, as a rule, have broad pelvises. The
characteristic differences between the male and female pelvis are
distinctly indicated as early as the fourth month of fetal life.
female, the superior ramus of the pubic bone is longer, increasing the
pubic/ischium ratio. The greater sciatic notch is wider and forms a longer
angle. The increased pubic length and laterally displaced ischia
result in a wider subpubic angle. The growth and remodelling of the
pubis produces extra bone at the symphysis, leaving a concave inferior
ramus, a ventral arc that represents a previous border of the symphysis, and
a narrow inferior pubic ramus. The female pubic symphysis is likely to
be longer in its superior-inferior diameter and smaller in its
dorsal-ventral diameters than is that of a male. Females are more
likely to have a well-developed preauricular sulcus, and those who have
borne children may have pits or guttering along the dorsal border of the
pubic symphysis. Since they have smaller femurs, females have smaller
acetabula, with males showing greater robusticity in this feature
corresponding to the generally greater size of the male femur head with
which it articulates.
greater sciatic notch is an often-used preliminary tool for sex
determination, though not the most accurate.
triangular shaped pubis with a broad medial aspect and no evidence of a
ventral arc is a characteristically male pattern. The female pattern
for these features is a rectangular pubis, pronounced ventral arc, and
sharp, narrow medial aspect of the ischiopubic ramus. According to
Bass, the presence of a ventral arc is the most diagnostic of the female
As a rule, the female sacrum is wider and flatter than that of the male,
permitting a greater outlet for the birth canal. However, this is a
rather subjective observation, and should only be used in conjunction with
other techniques of sex determination.
index = sacral anterior breadth X 100/divided by sacral anterior height)
of the Males and Female Pelvises:
massive; rougher; heavier
massive; smoother; more delicate
end of pelvis relatively vertical
end of pelvis tilted forward
projects further above sacroiliac joint
does not project as far above sacroiliac joint
and longer with pronounced sacral curvature
and wider with less curvature
movable; more vertical
movable; tilted backward
of greater pelvis
superior spines closer together; hips less flared
superior spines further apart; hips more flare
shaped, less space
to round shape, spacious
more laterally; larger
slightly anteriorly; smaller
angle usually less than 90 degrees (narrow)
than 100 degrees (wide)
ramus (ramus of ischium)
on the medial aspect
on the medial aspect
sulcus (depression between sciatic notch and sacroiliac
Dimorphism in the Human Pelvis
minimal overlap between the male and female ranges,
indicating that relatively few pelvises are ambiguously male or female)
Schultz 1949 and A & D 1990)
following diagrams compares the male and female pelvis, notice the
differences in the pelvises shown below, especially the much wider pubic
arch and birth canal (aka pelvic outlet/inlet) in the female. Also,
the ischia spines are less pronounced and significantly further apart in a
- in order to allow the the head of a baby to pass through.
Long Bones and other
In the adult skeleton, the long bones in the legs and arms can be examined
and differences in the diameter of the humeral
head, femoral head, and bicondylar breadth used for sex
determination, and sites of attachment for the deltoid and hamstring muscles
analysed for degree of robusticity. Interestingly, and rather
unexpectedly, the average female upper arm bone (humerus) is 1" (2.5
cm) longer than the
male upper arm - making it one of the most visually obvious signs of a male
or female to an informed observer. The short upper arm makes it easier for males to throw footballs
and lift heavy objects (less moment arm), the longer upper arm makes it
easier for females to hold and suckle babies.
length ratio has become a widely known form of sex differentiation.
Most men have an index finger (digit 2, or 2D) shorter than their ring finger
(digit 4, or 4D), whilst most women have an index finger that is as long or longer
than their ring finger. Significant deviation from a 2D to 4D ratio of
0.98:1 ratio is a
fairly strong indicator of natal sex.
It's believed that the difference
in finger length is due to
the action of "male" androgen hormones on the skeleton of a developing foetus. This seems to be confirmed by the fact that suffers of
Androgen Insensitivity Syndrome (who are genetically
XY male, but not affected by Androgen) often have a statistically female digit ratio, whilst women who
suffer from congenital adrenal hyperplasia (which raises their androgen
levels before birth) often have a statistically male ratio.
A young transsexual woman. On
initial impressions her petite frame indicates female,
but her large hands and longer ring finger give a strong hint.
Patrícia Araújo (born Felipe Silva de Araújo) shows of
that have made her a top female model in Brazil.
Ring finger (4D)
- longer than 2D
- shorter than 2D
weight is :
head of femur (mm)
oblique length (mm)
There is no
definite 100% way of distinguishing a male from a female skeleton, but here
is a list of the major criteria to be considered.
Penny Clifford had SRS at
about 31 - below the average age for a westerner. However
while obviously a very attractive woman, the lower picture shows
physical problems that face most adult transsexuals due to their
already masculinised skeleton.
Skull is heavy and
Lighter and smoother
Forehead is usually
Sinuses are large
Cranium is large
Smaller (by about 10%)
Mandible is large and
Lighter and smaller
Teeth are large
Upper arm is short
Upper arm is long
Ring finger longer than index finger
shorter than index finger
robust, heavy, rough
Broad, light, smooth
Pelvic inlet is heart
Oval to round shape
Iliac fossa is deep
Ilium extends further
above the sacrum
More vertical, lessabove the sacroiliac
Angle under the symphysis
is usually much less than 90 degrees
Angle is often greater than 100
Sacrum is long, with
a pronounced sacral curvature
Broad, short less
Coccyx points anteriorly
Bone weight is heavy
Bone markings are
Feminisation of the Male Skeleton
You may now
want to read the article on this site about
surgery on the genetic male.