1860s skiing had reached the U.S. state
of California. Ski-jumping competitions
began in the 1870s. Nordic skiing events
were a part of the firstWinter Olympics,
held in 1924.
Alpine skiing developed during the late
1800s and early 1900s. Alpine events
became a part of the Olympics in 1936.
Freestyle skiing and snowboarding are
newer events. Mogul and aerial skiing
were added to the Olympics in the
1990s. Snowboarding events were first
held at the 1998 Olympics.
#More to explore
Olympic Games
A snowboarder on a half-pipe course goes back and forth from one side of the half-pipe
to the other.
100 Skiing BRITANNICA STUDENT ENCYCLOPEDIA
Skin
Skin is the outer covering of humans
and all other animals with a backbone.
It protects the body from germs, injuries,
and extremes of hot or cold.
The skin of some animals has special
features that provide more protection.
Birds, for example, have feathers
attached to their skin. Fish and reptiles
have plates called scales over their skin.
Most mammals have a thick coat of hair
called fur. Humans have hair on their
skin, too, but not enough to act as protection.
Human skin has three layers. The epidermis
is the thin outer layer. Dead cells
of the epidermis constantly flake off as
new ones form. Cells in the epidermis
produce a substance called melanin.
Melanin creates different skin colors.
The epidermis has cells that make nails,
too.
The middle skin layer is called the dermis.
It is thicker than the epidermis,
which it supports and strengthens. The
dermis has fibers that make the skin
tough and stretchable. Pits in the dermis,
called follicles, make hair. The dermis
also contains blood vessels and
nerves. Nerves are fibers that send information
picked up by the senses to the
brain.
The third, deepest layer of the skin is
made up mostly of fat. This fat supplies
nutrients to the other two layers. It also
cushions the body and protects it from
the cold.
The body releases some substances
through the skin. Sweat glands send a
watery liquid called sweat through pores,
or tiny openings, on the skin’s surface.
Sweat cools the body. Other glands in
the skin produce an oil that can give the
skin a slightly greasy surface. This oil
helps keep the skin flexible.
Skin can be irritated or damaged in a
number of ways. Viruses can cause skin
blisters known as shingles. Extra oil production
can cause a condition called
acne. Skin burns can be caused by fire,
chemicals, electric shock, or the sun.
#More to explore
Acne • Burn and Scald • Feather • Hair
• Nail and Claw
Human skin has three layers: the epidermis,
the dermis, and a layer made mostly of fat.
Hair follicles, oil glands, sweat glands,
nerves, and blood vessels lie beneath the
surface of the skin.
BRITANNICA STUDENT ENCYCLOPEDIA Skin 101
Skopje
Population
(2004 estimate)
506,930
Skopje is the capital of Macedonia, a
country in southeastern Europe. The
city lies on the Vardar River. It is Macedonia’s
largest city by far.
Skopje is Macedonia’s center of business
and industry. Factories in the city process
foods, cement, metals, and other
products. Trade, banking, tourism, and
other services are also important.
People called the Illyrians founded Skopje
in ancient times. By the 300s the city
was the capital of a province of the
Roman Empire. In 518 an earthquake
destroyed the city, but it was rebuilt.
The Serbs conquered Skopje in 1189.
The Turkish Ottoman Empire controlled
the Macedonia area from 1392
until 1912.
In the early 1900s Skopje and the rest of
Macedonia became part of the country
of Yugoslavia. In 1963 an earthquake
destroyed most of the city. Skopje was
rebuilt with many modern buildings. In
1991 Macedonia became an independent
country. Skopje was its capital.
..More to explore
Macedonia
Skull
In animals with a backbone, including
human beings, the skull forms the hard
part of the head. It surrounds and protects
the brain. The skull is a part of the
body’s skeletal system.
The human skull must be large enough to
protect a large brain.
102 Skopje BRITANNICA STUDENT ENCYCLOPEDIA
The skull is made up of several bones
that are joined together like a jigsaw
puzzle. Many of the other bones of the
body meet at movable joints. The bones
of the skull, however, meet at joints that
do not move. (The lower jawbone,
which does move, is not really a part of
the skull.)
The cranium is the part of the skull that
covers the brain. The human cranium is
noticeably larger than the part of the
skull that makes up the face. In most
other animals the opposite is true—the
face is larger than the cranium.
Openings in the skull let air move
through the nose. Other openings form
eye sockets that support and protect the
eyes. The spinal cord, which is the
body’s main nerve, enters the skull
through an opening at its bottom.
Nerves from the eyes, the nose, the ears,
and the tongue pass through smaller
openings on their way to the brain.
The skull rests on the atlas, which is the
topmost vertebra, or bone, of the spine.
This allows the skull to nod up and
down. The atlas can turn on the vertebra
directly beneath it. This allows the skull
to turn from side to side.
..More to explore
