[This
article should be read in conjunction with the article on Average
Body Size.
I also 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
proportions.

Jessica is a very
beautiful woman, but a close inspection reveals male skeletal
characteristics. |
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
complete].
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:
 |
 |
A
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. |
A
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. |
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
confirm.

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. |
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.


Measurements of
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.
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.’ "
Skull
The adult
female skull retains gracile attributes seen in the pre-pubescent skull,
but the male cranium becomes markedly rougher in adulthood at the sites of
muscle attachment.
Major
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.

Phenotypic
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. |
Above
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.
The
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.
The
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
larger.
Finally,
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.
 |
Male and
Female Cranium Differences
Most
important skull differences between men and women are indicated by
the letter value on the figure to the left and described below:
A)
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:
Cranium
Feature
|
Male
|
Female |
Frontal
bone (forehead) |
lower
and sloping |
more
vertical and rounded |
Temporal
Ridge |
large |
small |
Bony
superciliary arches (browridges) |
prominent |
absent
or slight |
Mastoid
process (bone behind the ear) |
large |
small
* |
Supraorbital
margin (ridge above eye) |
rounded |
sharp |
External
occipital protuberance (protrusion on lower back of the cranium) |
generally
present |
generally
absent |
Nuchal
crest (low ridge along the back base of the cranium) |
rugged |
smoother,
even absent |
Zygomatic
process (cheek bones) |
extends
past external |
does
not * |
Mandible
(jaw) |
larger
and more robust |
smaller
and lighter |
Symphysis
and mental eminence of mandible (chin) |
square |
rounded
* |
Ramus
of mandible (back of jaw bone) |
straight |
slanting |
Mandible
gonion and gonion angle (back corner of jaw bone) |
flaring
and sharply angled |
less
so |
Sinuses
(air ways) |
larger |
smaller |
Teeth |
larger |
smaller |
Cranium |
deeper
and larger by about 10% |
smaller |
Total
skull |
heavier,
rougher |
more
rounded, smoother |
*These
may vary. Exceptions occur frequently.

An
ever increasing number of teenagers are having "gender confirmation"
hormone therapy.
The result is a reduction in the differentiation
between male and female skeletons.
This will become statistically
significant if 1% teenagers identify as being transgender,
which is very
probable based upon recent trends.
Face
Its worth
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
indications.
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.
In
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.
Forehead
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. Nose
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
than males.

Chin
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.

A woman's figure
would seem to be an obvious male/female differentiator - but
it's not, even with top models, due to the wide diversity.
Many teenage boys technically have a better figure than
their sister!
|
Physical Sex
Differences
The following
sex differences are true for the hypothetical "average" male and
female.
Genitals and
Functions
Males
have penises and testes; females have vaginas and wombs.
Form
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.
Head
Features
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.
Breasts and
Shoulders
Women have developed breasts with larger nipples and areolas than
men. Women's shoulders are more narrow, rounded, and sloping
than men's.
Angle of
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.
Hips and
Legs
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.
Hands and
Feet
Women's hands and feet are relatively smaller, narrower, and more
delicate looking than men's.
Hair
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.
Dimensions
Women are generally smaller and more delicate than men. The following
apply generally for those of western European descent:
Height
By age 20 years, women are generally 10 percent shorter than men.
Weight
By age 20, women are generally 20 percent lighter than men.
Strength
Adult
men are generally 50 to 60 percent stronger than women. |

An attractive
girl, but she is a XY transsexual and her skeleton -including her
pelvis - reflects this past. |
Pelvis
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.]
Factors
contributing to the overall shape of the pelvis are constrained by both
the demands of bipedal locomotion, as well as those for perpetuating the
human species - principally in relation to the requirements of childbirth.
It is usually impossible to
distinguish between the pelvis of a boy and a girl before puberty.
Thereafter - of
all bones - the
pelvis shows the greatest sexual differentiation and is thus a primary
tool for identifying male vs female skeletons post-puberty.

Exaggerated
images of female and male lower torso's
|
On average, the
adult 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.
A
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
pubic features.

A calculation of supposedly
ideal female proportions |
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. These characteristics all reach a maximum
in a woman's mid- to late-20's - just before her fertility starts to
decline significantly.
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.
As a result, women of a short stature tend to have obviously very broad
hips.
Sacrum
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.
Sacral
Index
(Sacral
index = sacral anterior breadth X 100/divided by sacral anterior height)
Race |
Male |
Female |
Australian
Aborigines |
100.2 |
110.0 |
Andamenese |
94.8 |
103.4 |
Egyptians |
94.3 |
99.1 |
Europeans |
102.9 |
112.4 |
Japanese |
101.5 |
107.1 |
Negroes |
91.4 |
103.6 |
Comparison
of the Males and Female Pelvises:
Pelvic
Feature
|
Male
|
Female |
General
appearance |
More
massive; rougher; heavier |
Less
massive; smoother; more delicate |
Tilt |
Upper
end of pelvis relatively vertical |
Upper
end of pelvis tilted forward |
Illium |
Deeper;
projects further above sacroiliac joint |
Shallower;
does not project as far above sacroiliac joint |
Sacrum |
Narrower
and longer with pronounced sacral curvature |
Shorter
and wider with less curvature |
Coccyx |
Less
movable; more vertical |
More
movable; tilted backward |
Width
of greater pelvis |
Anterior
superior spines closer together; hips less flared |
Anterior
superior spines further apart; hips more flare |
Pelvic
inlet |
heart
shaped, less space |
oval
to round shape, spacious |
Pubic
symphysis |
Taller;
rough |
Shorter;
smooth, moveable |
Greater
sciatic notch |
narrow |
wide |
Obturator
foramen |
large,
oval shaped |
small,
triangular shaped |
Acetabulum |
Faces
more laterally; larger |
Faces
slightly anteriorly; smaller |
Pubic
Arch |
Subpubic
angle usually less than 90 degrees (narrow) |
greater
than 100 degrees (wide) |
Subpubic
cavity |
no
ventral arc |
ventral
arc |
Ischiopubic
ramus (ramus of ischium) |
broad
on the medial aspect |
narrow
on the medial aspect |
Preauricular
sulcus (depression between sciatic notch and sacroiliac
articulation) |
uncommon |
common |
Sexual
Dimorphism in the Human Pelvis
(Note the
minimal overlap between the male and female ranges,
indicating that relatively few pelvises are ambiguously male or female)
|
n |
Mean |
Min |
Max |
Male |
50 |
79.9 |
71.0 |
88.0 |
Female |
50 |
95.0 |
84.0 |
106.0 |
(Source:
Schultz 1949 and A & D 1990)
The
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
female
- in order to allow the head of a baby to pass through.

Anterior (front) View |

Superior (Top) View |
Superimposing
diagrams of the adult female and male pelvis
at the same scale demonstrates the additional width of the later. As result the
average transwoman has narrower hips than the average cis-woman. This can
be visually disguised (see below left) by means of silicon hip and buttock implants, but
one serious problem remains...


Ava
Glasscott age 30, - just after having SRS. Height 5'
10", Weight 145 lbs, Figure 34-27-38, Cup size DD. The
reasons for her subsequent success as a female model (despite her
age) are self evident. |
The wider
pelvis of a woman results in the femur (upper leg bone) joining the hips to the knee at a
different (less vertical) angle than in men; that’s why women walk
slightly differently to men. Most notably women have a slightly
greater swinging of the hips and hold their arms out a little more for
balance and to keep space with their wider hips. The differences are
very subtle but evolution has made us all ultra-sensitive at
detecting male vs female characteristics, and a male rather than female gait
can be a give-away at a distance. Some transwomen put a lot of time and effort in
to "walking like a woman" but it's not a natural motion for their
skeleton, and is difficult and even uncomfortable to sustain.
Also, when consciously trying to trying to adopt a female gait, it's
all too easy to exaggerate this and arrive at a 'cat walk model' or 'gay
man' motion that actually attracts unwanted attention.

Born John Matheny, Las Vegas showgirl
Jahna Steele has
the slight skeletal build
common in women and rare in men.
Her height
(68 inches, or 173 cm) is
actually above average for a woman, but this PR photo disguises that. |
Long Bones and other
Bones
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.
Finger
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 off
legs
that have made her a top female model in Brazil.
|
Skeletal
Feature
|
Male
|
Female |
LEGS |
Femur
bone :
- Diameter
- Bicondylar
width
- Popliteal
length
- Trochanteric
oblique length
|
- greater
- greater
- longer
- longer
|
- lesser
- lesser
- shorter
- shorter
|
ARMS |
|
|
Humerus
bone :
|
|
|
FINGERS |
|
|
- Index
finger (2D)
-
Ring finger (4D)
|
- shorter
than 4D
- longer than 2D
|
- longer
than 4D
- shorter than 2D
|
BONES
(GENERALLY) |
Bone
weight is : |
heavier |
lighter |
Bone
markings : |
more
prominent |
less
prominent |
Measurements |
Female |
Probably
Female |
Indefinite
sex |
Probably
male |
Male |
Diameter
of
head of femur (mm) |
<41.5 |
41.5
to 43.5 |
43.5
to 44.5 |
44.5
to 45.5 |
>45.5 |
Trochanteric
oblique length (mm) |
<390 |
390
to 405 |
405
to 430 |
430
to 450 |
>450 |
Height
Height is a good indicator of sex, although a rapid
in increase in height over the 50 years due to better nutrient has confused the
statistics and age based percentiles. The following table indicates
some examples of the differentiation between average male and female heights in surveys taken
since 2003:
Country |
Age
Group |
Average Male Height |
Average Female Height |
Ratio |
U.K.
–
England |
16+ |
1.754 m (5 ft 9 in) |
1.619 m (5 ft 3 1⁄2 in) |
1.08 |
U.K. –
England |
16–24 |
1.771 m (5 ft 9 1⁄2 in) |
1.644 m (5 ft 4 1⁄2 in) |
1.08 |
U.K.
–
England |
25–34 |
1.776 m (5 ft 10 in) |
1.637 m (5 ft 4 1⁄2 in) |
1.08 |
U.K.
–
Scotland |
16+ |
1.750 m (5 ft 9 in) |
1.613 m (5 ft 3 1⁄2 in) |
1.08 |
U.K.
–
Scotland |
25–34 |
1.782 m (5 ft 10 in) |
1.635 m (5 ft 4 1⁄2 in) |
1.09 |
U.K.
–
Wales |
16+ |
1.770 m (5 ft 9 1⁄2 in) |
1.620 m (5 ft 4 in) |
1.09 |
U.S. |
All Americans, 20–29 |
1.776 m (5 ft 10 in) |
1.632 m (5 ft 4 1⁄2 in) |
1.09 |

Summary
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.
Male |
Female |


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
the
physical problems that face most adult transsexuals due to their
already masculinised skeleton. |
|
Height is
greater* (average 5ft 10 in) |
Height is lower*
(average 5ft 4in) |
Skull is heavy
and rough |
Lighter and
smoother
|
Forehead is usually
sloping |
More vertical |
Sinuses are large |
Smaller |
Cranium is large
|
Smaller (by about 10%) |
Mandible is large and
robust |
Lighter and smaller |
Teeth are large |
Smaller |
Upper arm is short |
Upper arm is long |
Ring finger longer than index finger |
Ring finger
shorter than index finger |
PELVIS |
Narrow,
robust, heavy, rough |
Broad, light, smooth |
Pelvic inlet is heart
shaped |
Oval to round shape |
Iliac fossa is deep |
Relatively shallow |
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
degrees |
Sacrum is long, with
a pronounced sacral curvature |
Broad, short less
curvature |
Coccyx points anteriorly
|
Points inferiorly |
Bone weight is heavy
|
Lighter |
Bone markings are
prominent |
Less prominent |
* Average adult
height in the "West", amazingly these figures have increased by over
an inch since World War 2, and two inches compared to pre-1900. |

Transsexual actress Claudia Cherriez.
An extraordinarily beautiful woman but still with male skeletal
characteristics. e.g. the length of her limbs and the shape of her
jaw bone. |
Surgical
Feminisation of the Male Skeleton
You may now
want to read the article on this site about
feminisation
surgery on the genetic male.
Height Analysis
I used to include a link here to a Java applet for
comparing your height against male and female averages. For example, at 5ft 9inches
I was boringly average as a man, but apparently only 3% of women were taller
- which was slightly hard to believe given all the women that seemed to
tower over me every day!
Unfortunately the applet hasn't been updated and it triggers
far too many security alerts to recommend. If anyone knows of an
alternative, please email me at
annie.richards@hotmail.com
|