There are 2 parietal bones like quadrangular plates. It has a raised section on the outer floor.

The frontal is a cranial bone shaped like an oyster. It has two eye sockets and a nose. It has two pairs of mounds. One pair on the forehead and the other pair on the eyebrows.

The bones of the skull that cover the brain are called calvarium. Bones are connected by suture joint. The stitches are called stitched stitches. There are 6 spaces or Fontanels in the skull. Due to the presence of fontanel, the shape of the baby’s head changes during delivery and it comes out easily through the birth canal. By the age of two, the baby’s carotid bones are completely fused by the suchar joints. Carotid artery is made up of 8 hard and flat bones.

The bones of the skull that cover the brain are called calvarium. Bones are connected by suture joint. The stitches are called stitched stitches. There are 6 spaces or Fontanels in the skull. Due to the presence of fontanel, the shape of the baby’s head changes during delivery and it comes out easily through the birth canal. By the age of two, the baby’s carotid bones are completely fused by the suchar joints. Carotid artery is made up of 8 hard and flat bones. The bones are:
(i) Frontal Bone: The frontal is a cranial bone shaped like an oyster. It has two eye sockets and a nose. It has two pairs of mounds. One pair on the forehead and the other pair on the eyebrows.
(ii) Parietal bones: There are 2 parietal bones like quadrangular plates. It has a raised section on the outer floor.
(iii) Occipital bone: The occipital bone surrounds the navel. It has a hole called Foramen magnum. The occipital bone consists of a shell part, 2 lateral parts and an occipital part. It connects the carotid with the atlas. (iv) Temporal bones: Two temporal bones exist on either side of the carotid. Each bone consists of four segments. squama, petromastoid, tympanic and styloid processes. In this bone the hearing organ, auditory canal, carotid canal and facial nerve canal are located.
(v) Ethmoid bone: Ethmoid is a spongy bone. It forms the eye socket and nasal septum. It consists of 6 plates. 1 transverse plate, 1 vertical plate, 2 orbital plates and 2 labyrinth plates. Each labyrinth plate contains tiny air chambers.
(vi) Sphenoid bone: Sphenoid is the bone forming the carotid floor. It looks like a bat or a butterfly. It consists of a body stem and 3 pairs of appendages. Its parts are the greater wing, the lesser wing and the pterygoid process.

Carotid and facial bones together are called cranium. It consists of 22 bones in total. The bones of the skull are – carotid, facial bone, cochlear and vocal cord or hyoid.
1. Cranium: The bones of the skull that cover the brain are called calvarium. Bones are connected by suture joint. The stitches are called stitched stitches. There are 6 spaces or Fontanels in the skull. Due to the presence of fontanel, the shape of the baby’s head changes during delivery and it comes out easily through the birth canal. By the age of two, the baby’s carotid bones are completely fused by the suchar joints. Carotid artery is made up of 8 hard and flat bones. The bones are:
(i) Frontal Bone: The frontal is a cranial bone shaped like an oyster. It has two eye sockets and a nose. It has two pairs of mounds. One pair on the forehead and the other pair on the eyebrows.
(ii) Parietal bones: There are 2 parietal bones like quadrangular plates. It has a raised section on the outer floor.
(iii) Occipital bone: The occipital bone surrounds the navel. It has a hole called Foramen magnum. The occipital bone consists of a shell part, 2 lateral parts and an occipital part. It connects the carotid with the atlas. (iv) Temporal bones: Two temporal bones exist on either side of the carotid. Each bone consists of four segments. squama, petromastoid, tympanic and styloid processes. In this bone the hearing organ, auditory canal, carotid canal and facial nerve canal are located.
(v) Ethmoid bone: Ethmoid is a spongy bone. It forms the eye socket and nasal septum. It consists of 6 plates. 1 transverse plate, 1 vertical plate, 2 orbital plates and 2 labyrinth plates. Each labyrinth plate contains tiny air chambers.
(vi) Sphenoid bone: Sphenoid is the bone forming the carotid floor. It looks like a bat or a butterfly. It consists of a body stem and 3 pairs of appendages. Its parts are the greater wing, the lesser wing and the pterygoid process.
2. Facial skeleton
The front and lower part of the carotid body is called the face. It consists of 14 bones in total. The facial bones are:
(i) Nasal bone: It is a rectangular bone. It forms the bridge of the nose.
(ii) Nasal Concha: A pair of thin and curved bones located on either side of the nasal cavity are the nasal concha.
(iii) Vomare: It is a quadrangular plate like bone. It forms the NASA interface.
(iv) Palatine bone: It forms the roof of the nose and the wall of the nasal cavity.
(v) Lacrimal bone: It consists of a lacrimal shaft, lacrimal sac and nasolacrimal duct.
(vi) Zygomatic bone: It is a quadrangular bone. It consists of an elevated part called the zygomatic arch.
(vii) Maxilla: The upper jaw consists of two equal maxillae. Right and left maxilla. It has four amplifiers. These are – zygomatic, palatine, frontal and alveolar.
(viii) Mandible: Mandible is the lower jaw. It looks U shaped. It consists of a trunk and 2 branches. It has two amplifiers. Coronoid and condyloid.
3 | Ear Ossicles
There are 3 small bones in the middle ear. These are-
(i) Malleus: It looks like a hammer. One end is attached to the tympanic membrane and the other end to the incus.
(ii) Incus : It looks like anvil. One end is attached to the malleus and the other end to the stapes.
(iii) Stepis: Stepis looks triangular or like a horse’s stirrup. It is the smallest bone in the human body. One end is attached to the incus and the other end to the fenestra ovalis.
4. Hyoid Bone
The U-shaped bone between the lower jaw and the larynx is called the hyoid. It consists of a body stem and 4 cornua. Its middle part is called body or hyoid body. There are two small cornua on either side of the body and two large cornua on the back.

The bones and cartilages of the skeletal system that lie along the axis of the body and support and protect the brain and soft organs of the body cavity are called axial skeleton. It consists of 80 bones. Axial skeleton consists of Skull, Vertebral and Thoracic case.

Skull
Carotid and facial bones together are called cranium. It consists of 22 bones in total. The bones of the skull are – carotid, facial bone, cochlear and vocal cord or hyoid.
1. Cranium: The bones of the skull that cover the brain are called calvarium. Bones are connected by suture joint. The stitches are called stitched stitches. There are 6 spaces or Fontanels in the skull. Due to the presence of fontanel, the shape of the baby’s head changes during delivery and it comes out easily through the birth canal. By the age of two, the baby’s carotid bones are completely fused by the suchar joints. Carotid artery is made up of 8 hard and flat bones. The bones are:
(i) Frontal Bone: The frontal is a cranial bone shaped like an oyster. It has two eye sockets and a nose. It has two pairs of mounds. One pair on the forehead and the other pair on the eyebrows.
(ii) Parietal bones: There are 2 parietal bones like quadrangular plates. It has a raised section on the outer floor.
(iii) Occipital bone: The occipital bone surrounds the navel. It has a hole called Foramen magnum. The occipital bone consists of a shell part, 2 lateral parts and an occipital part. It connects the carotid with the atlas. (iv) Temporal bones: Two temporal bones exist on either side of the carotid. Each bone consists of four segments. squama, petromastoid, tympanic and styloid processes. In this bone the hearing organ, auditory canal, carotid canal and facial nerve canal are located.
(v) Ethmoid bone: Ethmoid is a spongy bone. It forms the eye socket and nasal septum. It consists of 6 plates. 1 transverse plate, 1 vertical plate, 2 orbital plates and 2 labyrinth plates. Each labyrinth plate contains tiny air chambers.
(vi) Sphenoid bone: Sphenoid is the bone forming the carotid floor. It looks like a bat or a butterfly. It consists of a body stem and 3 pairs of appendages. Its parts are the greater wing, the lesser wing and the pterygoid process.
2. Facial skeleton
The front and lower part of the carotid body is called the face. It consists of 14 bones in total. The facial bones are:
(i) Nasal bone: It is a rectangular bone. It forms the bridge of the nose.
(ii) Nasal Concha: A pair of thin and curved bones located on either side of the nasal cavity are the nasal concha.
(iii) Vomare: It is a quadrangular plate like bone. It forms the NASA interface.
(iv) Palatine bone: It forms the roof of the nose and the wall of the nasal cavity.
(v) Lacrimal bone: It consists of a lacrimal shaft, lacrimal sac and nasolacrimal duct.
(vi) Zygomatic bone: It is a quadrangular bone. It consists of an elevated part called the zygomatic arch.
(vii) Maxilla: The upper jaw consists of two equal maxillae. Right and left maxilla. It has four amplifiers. These are – zygomatic, palatine, frontal and alveolar.
(viii) Mandible: Mandible is the lower jaw. It looks U shaped. It consists of a trunk and 2 branches. It has two amplifiers. Coronoid and condyloid.
3 | Ear Ossicles
There are 3 small bones in the middle ear. These are-
(i) Malleus: It looks like a hammer. One end is attached to the tympanic membrane and the other end to the incus.
(ii) Incus : It looks like anvil. One end is attached to the malleus and the other end to the stapes.
(iii) Stepis: Stepis looks triangular or like a horse’s stirrup. It is the smallest bone in the human body. One end is attached to the incus and the other end to the fenestra ovalis.
4. Hyoid Bone
The U-shaped bone between the lower jaw and the larynx is called the hyoid. It consists of a body stem and 4 cornua. Its middle part is called body or hyoid body. There are two small cornua on either side of the body and two large cornua on the back.

The skeletal system is divided into two parts.
1. Exoskeleton: The skeletal system that is visible from outside the body is called exoskeleton. Nails, teeth, hair etc. belong to this tantra.
2. Endoskeleton: The skeleton that forms the internal structure of the body is called endoskeleton. The human skeletal system is divided into two main parts. Axial skeleton and appendicular skeleton.

1. Bone: Bone is composed of hard cartilage and calcium.
2. Cartilage: Cartilage or soft bone is composed of soft cartilage and chondrin. It does not contain calcium.
3. Ligaments: Ligaments connect one bone to another bone. It is dense, white fibrous and elastic. It holds various organs in proper place.
4. Tendon: Tendons are located at the ends of muscles and connect bones and muscles. It is dense, strong, whitish, flexible and inelastic.
5. Joint: Two or more unstable meeting points are joints. It facilitates movement, movement, bearing and function of various organs.

1. Formation of body structure: Skeletal system forms the body structure and gives specific shape to the body.
2. Preservation: The skeletal system protects the soft organs of the body such as the heart, lungs, brain, spinal cord, etc.
3. Movement: The skeletal system controls the movement of the body through the contraction and expansion of muscles.
4. Red blood cell production: The main blood producing tissue is the red bone marrow. Red blood cells are produced from the bone marrow of the crown, sternum, thorax, vertebrae, humerus and femur. An average of 26 lakh red blood cells are produced from the bone marrow every second. Macrophages are also produced from red bone marrow.
5. Immunity: Stabilized reticuloendothelial system increases the body’s immune system.
6. Breathing and Hearing: The thorax helps in breathing and the cochlea helps in hearing.
7. Mineral salt storage: Skeletal bones store calcium, phosphorus, potassium etc. About 97% of the body’s calcium is stored in bones.
8. Accumulation of toxic elements: If the body contains toxic elements such as lead, arsenic, etc., the bones store them.
9. As a junction: Acts as a junction of muscles, ligaments and tendons.
10. Pressure and ionic balance: Maintains internal pressure and ionic balance of the body.
11. Hormonal action: Osteocalcin hormone is produced from bone cells. This hormone regulates blood sugar and fat levels.
12. Chemical energy storage: With age, the red bone marrow of the human body changes into yellow bone marrow. Adipose cells are present in pale bone marrow. Adepose cell acts as a reservoir of chemical energy.

The system made up of bone and cartilage derived from the embryonic mesoderm that forms the body structure, carries the weight of the body, attaches muscles and protects the soft parts of the body is called the skeletal system. It is made up of 206 bones. The skeletal system accounts for 15% and 10% of the total body weight of men and women respectively. Volatility density is highest at 21 years of age. The branch of biology that deals with human bones is called Human osteology.