Question

The pivot joint between atlas and axis is a type of
a. Saddle joint
b. Fibrous joint
c. Cartilaginous joint
d. Synovial joint

Answer 1

Hint: A joint is defined as the meeting place between bones and cartilages or between two bones. The three main types of joints in the body are- sutures, symphysis and synovial joints.

Complete answer:
> Option A: Saddle joint- These are also called biaxial joints and they allow movement in two planes but movements are free. In this the projection of one bone fits upon the saddle or depression of another bone, e.g. joints of carpals of thumb with metacarpal permit movement in two planes.

> Option B: Fibrous joints- These are immovable joints that have two bones fixed together either through fibres or cement or sutures. They are of different types- sutures, gomphosis, shindylases, and syndesmoses.

> Option C: Cartilaginous joint- These are slightly movable joints which are mediated through fibrous cartilage, for example- Pubic symphysis, intervertebral disc of mammal.

> Option D: Synovial joints- These are the types of joints in which one bone forms a knob like swelling while other bone forms a depression. The ends of both the bones are covered with articular cartilages. These joints are found between limb bones.
They are of following types:
- Ball or socket joint or enarthrosis
- Hinge joint or gingulum
- Angular or ellipsoidal joint
- Pivot or rotatory joint
- Gliding or condyloid or arthrodial joints
- Saddle joint
Pivot joints are also called rotatoria or trochoid. In this one bone acts as an axle and the other acts as a ring acting upon the axle e.g. atlas and axis of mammal.

Hence, the correct answer is option (D).

Note: In the synovial joint between the two bones, there is a synovial cavity filled with a gelatinous synovial fluid bounded by a fibrous synovial membrane. Synovial fluid lubricates the joints for their free movement.