Page 25 - Viva ICSE Science 5 : E-book

8 bones make up a protective frame around the brain and the
remaining 14 bones make the upper and lower jaws, and other facial
structures. Except the lower jaw, all other bones in the skull are fi xed

and hence, immovable. We are able to talk and eat because of the
movable lower jaw.
Skull

Limbs

Human beings have two pairs of limbs—the forelimbs or the arms and the hindlimbs or
the legs.

Forelimbs

Forelimbs or the arms are divided into two parts—the upper
arm and the lower arm. The upper arm has a single long bone
humerus
called humerus, whereas the lower arm has two long, parallel
bones called ulna and radius. Humerus is joined to ulna and radius
radius at the elbow. Many small bones join together to make
ulna
up the wrist.

Forelimbs along with the muscles and joints provide
movement to arms and help us to perform diff erent activities

like write, eat and hold things.
Forelimb

Hindlimbs

Hindlimbs or the legs are also divided into two parts—the

upper leg and the lower leg. The thigh bone, known as femur,
present in the upper leg is the longest bone in the body. The

lower leg has two long, parallel bones called tibia and fi bula. femur
Femur is joined to tibia and fi bula at the knees. Many small
bones join together to make up the ankle and the foot.

Forelimbs along with the muscles and joints provide f ibula
movement to legs and help us to perform diff erent activities
like walking, running, standing and jumping. Femur, which is tibia

also the strongest bone of the body, supports body weight
during these activities.
Hindlimbs

11