homework encyclopedia

130

The skeleton is the inner framework of. BONES that

supports and gives shape to the human body. It also

protects some of the soft organs of the body – for

example, the skull surrounds the brain. Muscles and

ligaments pull on the bones of the skeleton at. JOINTS

to make the body move.

HOW DOES A SKELETON GROW?

A newborn baby has more than 300 bones, but many

are made of a soft, rubbery material called cartilage

instead of bone. Up until the late teens, as a child

grows the cartilage lengthens and turns into bone,

and some bones fuse together. By adulthood, there

are just 206 bones in the skeleton.

ARE BONES DRY?

Dead bones are dry and

brittle, but living bones feel

wet and a little soft. They

are also slightly flexible, so

they can absorb pressure.

Like most parts of the body,

bones have a network of

blood vessels and nerves

running through them, and

they bleed when broken. Up

to one third of the weight of

a living bone is water.

HOW STRONG ARE BONES?

Weight for weight, bone is five

times stronger than steel, but it

is very light. The skeleton makes

up only one sixth of an adult’s

weight. The skull in particular

is very strong, because it has to

protect the brain and sense organs,

such as the eyes, ears, and nose.

4 THE HUMAN SKELETON

Each bone in the body has a scientific

name, but many also have everyday

names. The largest is the femur, or

thigh bone, and the smallest are the

tiny ossicle bones in the inner ear.

More than half the bones of an adult’s

skeleton are in the hands and feet.

SKULL BONES 1

This coloured X-ray of the skull

has an image of the brain placed

over it to show the fit. The skull is

made up of 22 separate bones, all

locked together by immovable

joints, except for the lower jaw.

GROWING HANDS 3

The first X-ray shows the gaps between the bones in a baby’s

hand that are filled with cartilage. By age 20, the finger

bones have grown longer and ossified (turned to bone).

Skeleton

The cranium,

the part of the skull

that protects the

brain, is made up

of eight bones fused

tightly together

The lower jaw,

or mandible, is

the only large

freely moving

bone in the skull

The fingers

are now made of

mature, hard bone

HAND OF A

ONE-YEAR-OLD

Clavicle

(collarbone)

Lumbar

(lower back)

vertebrae

HAND OF A

20-YEAR-OLD

Cartilage outline

is just visible

Radius

(thumb side

forearm bone)

Scapula

(shoulder

blade)

Phalanges

(toe bones)

Ulna

(forearm bone)

Metatarsals

(foot bones)

Cervical

(neck)

vertebrae

Metacarpals

(palm bones)

Pelvis

(hip bone)

Carpals

(wrist bones)

Tibia

(shin bone)

Humerus

(upper arm

bone)

Tarsals

(ankle bones)

Sternum

(breastbone)

Cranium

(skull)

Fibula

(calf bone)

Femur

(thigh bone)

Phalanges

(finger

bones)

Mandible

(lower jaw)

Patella

(kneecap)

Ribs

skeleton