BACKGROUND INFORMATION
THE HUMAN SKELETON
The human skeleton is comprised of 206 bones, half of which are in the hands and feet.
These bones are articulated (connected) to make what is known as an endoskeleton (an
inside skeleton). Endoskeletons give humans protection for their internal organs and allow
freedom of movement.
The human skeleton serves several purposes:
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Protection of vital organs
Place of attachment for muscles
Gives form to our overall body
Supports the rest of the body
Bones are alive. They are made up of living cells. Thirty percent of bone is living tissue, cells,
and blood vessels. Forty-five percent of bone is mineral (calcium and phosphorus), giving
bone its hardness. The remaining 25% of bone is water.
femur
TYPES OF BONES
There are four types of bones.
1. Flat Bones: These bones provide broad surfaces for anchoring of muscles and protect
other structures of the body. Examples of flat bones are facial bones, shoulder bones
(scapula), and ribs.
scapula
2. Long Bones: Long bones form the levers of our arms and legs. Examples are the
humerus (upper arm) and the femur.
Humerus
3. Short Bones: These create strong, compact structures, such as in the wrists and ankles.
Other examples are the phalanges (fingers).
phalanges
4. Irregular Bones: These are the bones that are shaped differently enough that they
cannot be grouped with the other three types of bones. The vertebrae (spinal bones)
are examples of this type of bone.
cervical vertebrae
HOW BONES ARE FORMED
The bones are articulated (connected) to other bones at the joints. There are five types of
joints. They are:
1. Hinge Joints: an example is the elbow
2. Ball and Socket Joints: an example is the pelvis
3. Pivot Joints: an examples is the head and neck
4. Gliding Joints: examples are the vertebrae
5. Immovable Joints: an example is the skull
The bones of the joints are held together by tough, rubbery strands of connective tissue
called ligaments. Muscles are attached to bones by rubbery strands of connective tissue
called tendons.
The joints are cushioned by tough connective tissue called cartilage. Your ears and the tip
of your nose are composed of cartilage. Also there is a liquid present in your moveable joints
called synovial fluid. This liquid reduces grinding of bone against bone in joints by lessoning
friction (much like oil reduces friction between moving machine parts.)
FORENSICS
Forensics is the science used to analyze physical evidence in legal proceedings. Most large
law enforcement agencies, including the FBI, employ forensic scientists to help solve crimes.
Knowing the exact physical dimensions of a crime victim is helpful in trying to identify that
victim. When a skeleton (or part of a skeleton) is found, the forensic scientist uses the
condition, the characteristics, and the length of certain bones to help determine the age,
weight, height, and gender of the victim.
BONE LENGTH
The forensic scientist uses certain bones to calculate the height of the skeleton when only a
partial skeleton is found. The bones that are used are the femur ( ), the tibia ( ), the
humerus ( ), or the radius ( ). The length of any one of these bones can be used to
determine height using the formulas below. (These measurements are in centimeters.)
How to Calculate the Height of a Male
Height= (femur x 2.23) + 69.08
Height= (tibia x 2.39) + 81.68
Height= (humerus x 2.97) + 73.57
Height= (radius x 3.65) + 80.40
How to Calculate the Height of a Female
Height= (femur x 2.31) + 61.41
Height= (tibia x 2.53) + 72.57
Height= (humerus x 3.14) + 64.97
Height= (radius x 3.87) + 73.50
A much less precise way of determining an approximate height is related to the length of
armspan, fingertip to fingertip (with both arms stretched out away from the body). The
relationship between armspan and height can vary.
A person can be a “square”: armspan is same as height.
A person can be a “tall rectangle”: height is a little more than armspan.
Or, a person can be a “short rectangle”” height is a little less than armspan.
GENDER DIFFERENCES
In male skeletons, the larger bones such as the tibia and ulna have sharper edges than the
same bones in most female skeletons. This is caused by the rubbing of tendons and muscle
tissue against the bones of the more heavily muscled males.
The ribcage of males is wider and larger than the ribcage of females. About one person in
twenty has an extra rib. The extra rib is more common in males than in females.
In general, a male’s shoulders are wider than a female’s shoulders.
male
female
The pelvis of the female is wider than that of the male. It must be able to accommodate a
growing fetus during pregnancy.
There is another gender difference that occurs less consistently. In the male hand, the index
finger (finger next to the thumb) is sometimes shorter than the third finger. In females, the
opposite is sometimes true; the first finger is longer than the third finger. (This gender
differences does not seem to occur often enough to truly be considered a difference.)
male
female
The openings in the skull for the eyes (called eye orbits) are different for males and females.
For males, the eye orbit is rectangular. For females, the eye orbits are more round.
male
female
OTHER DIFFERENCES IN SKELETONS
Aging
Ossification is the process in which calcium is deposited over the bone to make it hard. Most
bones are completely ossified by the time a person reaches twenty years of age. Old bones
show signs of calcium loss, lose flexible bone tissue and become brittle. Brittle bones are
more easily broken.
Athletes
Often the flared end of the femur (thigh bone) of athletes is much larger than that of the
average person due to the extreme stress placed on that part of the bone during athletic
activities.