Skull bones protective covering for the brain
The skull provides the bony framework for the soft tissues of the face and also secure enclosures for eyes and the master of all organs-the brain. It is not a single bone but consists of several bones some paired and some single cleverly joined by nature with remarkable imagination and superb craftsmanship. The skull can be divided into two parts-the cranium which contains and protects the brain and the facial skeleton which provides the bony framework for the soft tissues of the face. The cranium is made up of eight bones. They are
2. Parietal bone
3. Sphenoid bone
4. Nasal bone 5. Zygomatic bone
6. Vomer bone 7. Maxilla
8. Mandible Left side of skull
Frontal bone: This is situated in front and is a single bone. It contributes to the entire forehead and the upper border and the roof of the orbits-the cavities which contain the eyes and the roof of the nasal cavity. The frontal bone contains air filled cavities known as frontal sinus.
The frontal bone articulates (to articulate means to form a joint with another bone) with the sphenoid, ethmoid, two parietals, two maxillae, two nasals, two lacrimals and two zygomatic bones. Parietal bones: There are two of them. They are roughly quadrilateral in shape. They form the sides and roof of the cranium. The outer surface is convex and the inner concave.
Each parietal bone articulates with the opposite parietal bone (this joint forms the sagittal suture that is felt as a narrow gap in a newborn baby), the frontal in front (this joint forms the coronal suture felt as a narrow gap in newborn babies), the occipital at the back (forming lamboidal suture), temporal bone at the side and with sphenoid bone at the lower angle in front. Click here to take the health quiz Occipital bone: This bone is situated at the back and the lower part of the cranium and is a single bone. This has a big opening called foramen magnum through which the spinal cord comes down into the spinal canal. This bone articulates with the two parietal bones in front, two temporal bones, the sphenoid and the atlas (the first cervical vertebra).
Temporal bones: They are two in number one on each side of the skull. They also contribute to the base of the skull. Each temporal bone articulates with the parietal bone, occipital, sphenoid, zygomatic and mandible. The upper expanded part is called the squamous part. A part of temporal bone can be felt behind the ear. This is called the mastoid process.
Another part called the petrous part contains the structures necessary for hearing. This is the hardest bone in the body (the hardest structure in the body is the enamel of tooth). The tympanic part forms the bony wall of the external ear canal through which sound waves enter the ear.
Ethmoid bone: unlike other bones this bone is spongy and light. It is situated in the front portion of the base of the cranium and is a single bone. It is in between the orbits and contributes to the roof of the nose.
It has a horizontal plate called the cribriform plate forming the roof of the nose. This plate articulates with the frontal bone in front. The fibers of the olfactory nerve pass through this plate on their way to the brain. A vertical (perpendicular) plate of this bone comes down from the horizontal plate and contributes to the formation of nasal septum-the plate like structure in between the two nostrils.
Attached to the horizontal plate on each side is a mass of irregular bone called the labyrinth. The outer surface of labyrinth contributes to formation of that wall of the orbit towards the nose. The inner surface of the labyrinth forms part of the side wall of the nasal cavity. Sphenoid bone: This bone has a peculiar shape. It looks somewhat like a bat with its wings fully spread. It is a single bone. It has a bony mass in the middle and two large wing like extensions (great wings) and two small wing like extensions. The central portion or the body contains two air filled cavities called sphenoidal sinuses separated from each other by a layer of bone. The pituitary gland which controls the functions of all other endocrine glands sits on the upper surface of the body. Upper surface of the sphenoid bone. Please click on the graphic for enlarged view.
The great wing on each side contributes to the lateral wall of the orbit. The small wing on each side contributes to the roof of the orbit. Lower surface of the sphenoid bone. Please click on the graphic for enlarged view.
Articulations: The sphenoid bone is situated near the center of the base of the skull. Hence it articulates with other bones on all sides. In front it articulates with the frontal, ethmoid and vomer bones. Behind it joins with the occipital bone. It also articulates with parietal, temporal, zygomatic and palatine bones of both sides. Interior of skull. Please click on the graphic to see enlarged view
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