Muscle is a band or bundle of fibrous tissue in a body that has the ability to contract, producing movement or maintaining the position of parts of the body.

i) Cranium is the part of our skull that encloses the brain.
ii) It is composed of 8 skull bones fixed together.

The skeleton is the hard structure or framework to the human body which supports and protects the body. It is composed of connective tissues like bones, cartilage, tendons and ligaments.

(i) It provides structure and shape to the body.
(ii) It supports and surrounds the internal organs of the body.
(iii) Calcium and phosphorous, the two minerals that the body needs for important regulatory functions, are stored inside the bones.
(iv) Red blood cells are produced in the bone marrow.
(v) The bones of the skeletal system act as levers for muscular action. Muscular movement would not be possible without tendons and ligaments.

► Muscles often work in pairs which work against each other. These are called antagonistic pairs.
► The two muscles, the biceps and triceps are working against each other.
►When the biceps contracts the lower arm is raised and the arm bends. In this position the triceps muscle is relaxed.
► To straighten the arm the reverse happens. The triceps contracts straightening the arm, while the biceps relaxes.

There are three types of movements:
a) Amoeboid movement
It is brought about by pseudopodia which are appendages which move with the movement of protoplasm within a celle
b) Ciliary movement
This movement is brought about by appendages called as cilia which are the hair like extensions of the epithelium. Both these kinds of movements are seen with cells of the lymphatic system
c) Muscular Movement
It is a more complex movement which is brought about by the musculoskeletal system. This type of movement is seen in the higher vertebrates.

The different types of joints are as follows: 
(i) Immovable joints - Example: Bones of the skull box .
(ii) Partially movable joints - Example: Joints between the ribs and breast-bone.
(iii) Freely movable joints - Example: Hip joint.
(iv) Gliding joint - Example: Ankle bones.
(v) Pivot joint - Example: Joint between axis vertebrae and atlas.
(vi) Hinge joint - Example: Joint between finger bones and toes.
(v) Ball and socket joint - Example: Shoulder joint.