Theory:

Introduction:
The skeletal system of comprises of bones, cartilages and joints. The bones of the skeletal system provides a framework of the body.
 
The movement of the animals or the human body occurs in a variety of ways. Certain parts of the body can be moved in various directions, and some features can be moved only in one direction.
 
All these movements and their variations are because of the bones that are attached by joints. The bones along with the muscles help in movements such as walking, running, chewing and so on.
The bones found in the body of humans form a framework known as the skeleton that gives shape to the body.
Human skeletal system:
The skeleton is a structural framework of bones which are linked together by joints. In humans, there are around \(305 \)bones at birth. With the increase of age, some of the bones fuse resulting in only \(206 \)bones, a few cartilages and a few ligaments and tendons that make up the skeleton.
 
The ligaments are structures that help in connecting the bones to the muscles. The human skeleton is divided into the:
  1. Axial skeleton
  2. Appendicular skeleton
Axial skeleton:
The axial skeleton forms the upright axis of the body that includes,
  • Skull
  • Vertebral column
  • Rib cage make up the axial Skeleton.
Axial_skeleton_diagram.svg
Axial skeleton system
  
1. Skull:
 
skull-41557.png
Human skull - Side View
 
The skull is a structure that is made up of many bones known as the cranial bones and facial bones. These bones are joined together to enclose and protect the brain and the structures of the face.
 
The hyoid bone that is found at the base of the buccal cavity and the auditory ossicles such as Malleus, Incus and Stapes are also included in the skull. The lower jaw bone is the largest and the strongest bone in the human face.
 
Important!
The stapes is the smallest bones in the body. Approximately it is \(2.8\)millimeters long.
2. Vertebral column:
  
1024px-Figure_38_01_07.jpg
Vertebral column
 
It is also known as the backbone. It extends from the base of the skull and consists of many small bones calledvertebrae that are \(33 \)in number and are serially arranged. 
The vertebral column protects the spinal cord. A person can bend over only due to the presence of this bone.
3. Rib cage:
  
Figure_38_01_08.jpg
Rib cage
 
There are \(12 \)pairs of curved and flat rib bones on each side of the chest that are joined to the central chest bone and the backbone.
 
They enclose the important delicate organs such as the lungs and the heart.
Appendicular skeleton:
The appendicular skeleton includes the pelvic and pectoral girdles and the bones of the limbs of the arm and leg.
 
1024px-Appendicular_Skeleton.png
Appendicular skeleton system
 
1. Limbs:
  
Humans have two pairs of limbs. They are the upper limbs also known as the fore limbs and the lower limbs that are also known as the hind limbs.
 
The fore limbs are used for various functions such as holding, writing, etc., and the hind limbs are used for walking, sitting etc.,
Some of the bones of the arms are the shoulder bones and the carpels.
The two prominent bones on the back are known as the shoulder bones and the bones of the wrist, and the palm are known as the carpels. One can fold their fingers only due to these carpels.
 
Lower and upper.png
Upper and Lower limbs
  
Important!
The thigh bone called the femur is the longest bone in the body.
Girdle:
The fore limbs and the hind limbs are attached to the axial skeleton by the pelvic and pectoral girdles.
 
1. Pelvic bone:
  
512px-Pelvic_girdle_illustration.svg.png
Pelvic gridle
 
It's a structure that protects the parts of the body below the stomach. It supports sitting correctly.
 
2. Pectoral girdle:
  
1024px-Figure_38_01_10.jpg
Pectoral gridle - Front and back view
 
The appendicular skeleton's bones link to the arm on either side, forming the shoulder girdle, also known as the pectoral girdle.
Other structures of skeleton system:
Cartilage and muscle are two additional structures that are part of the skeletal system.
1. The soft structure found in between the joints of the skeleton and the upper portion of the ear lobe is known as a Cartilage.
2. The soft contractile tissue that is attached to the bones is known as Muscle.
What are joints?
Have you ever wondered how we are able to bend and rotate our body parts? It is because of the joints present in our body.
The connection between two bones in the skeletal system is a joint.
Bones are rigid structures that cannot be bent or rotated. But still, we can do so with the help of joints. Hence, joints play a prominent role in the movement and locomotion of animals such as humans.
Not all the parts of the body can be moved easily. Only the places where two bones join together can be moved easily. These places known as joints.
Reference:
https://commons.wikimedia.org/wiki/File:Axial_skeleton_diagram_ro.svg
https://commons.wikimedia.org/wiki/File:Figure_38_01_07.jpg
https://commons.wikimedia.org/wiki/File:Figure_38_01_08.jpg
https://commons.wikimedia.org/wiki/File:Appendicular_Skeleton.png
https://upload.wikimedia.org/wikipedia/commons/3/32/Figure_38_01_13.jpg
https://commons.wikimedia.org/wiki/File:Arm_Bones.png
https://commons.wikimedia.org/wiki/File:Figure_38_01_10.jpg
https://commons.wikimedia.org/wiki/File:Pelvic_girdle_illustration.svg