The Skull

The brain is the highest seat of intelligence.

The Head and neck are the uppermost part of the body.  The Head comprises the skull and lodges the brain covered by meninges, hypophysis cerebri, special senses, teeth, and blood vessels. Bones of the head and neck include the skull, i.e. cranium with mandible, seven cervical vertebrae, the hyoid, and six ossicles of the ear.

The skull cap is formed by frontal, parietal, squamous temporal, and a part of occipital bones, develop by intramembranous ossification, being a quicker one-stage process. The weight of the brain is not felt as it is floating in the cerebrospinal fluid. Our personality, power of speech, attention, concentration, judgment, and intellect are because of the brain that we possess and its proper use.

What is called the skull?

The Skeleton of the head is called the skull. It consists of several bones that are joined together to form the cranium. The term skull also includes the mandible or lower jaw which is a separate bone. However, the two terms skull and cranium, are often used synonymously.

The skull can be divided into two main parts:

• The calvaria or brain box is the upper part of the cranium which encloses the brain.
• The facial skeleton constitutes the rest of the skull and includes the mandible. 

How many bones are there in the human skull?

The human skull consists of 28 bones and divided into two parts calvaria and facial skeleton some of them is paired and some of them are not paired, which are named as follows:

1. Calvaria

The calvaria or braincase is composed of 14 bones including 3 paired ear ossicles.

Paired

• Partial (2)
• Temporal (2)
• Malleus (2)
• Incus (2)
• Staps (2)

Unpaired

• Frontal (1)
• Occipital (1)
• Sphenoid (1)
• Ethmoid (1)

2. Facial skeleton

The facial skeleton is composed of 14 bones.

Paired

• Maxilla (2)
• Zygomatic (2)
• Nasal (2)
• Lacrimal (2)
• Palatine (2)
• Inferior nasal concha (2)

Unpaired

• Mandible (1)
• Vomer (1)

Skull Joints

The joints in the skull are, mostly sutures, a few primary cartilaginous joints, and three pairs of synovial joints. Two pairs of synovial joints are present between the ossicles of the middle ear. One pair is the largest temporomandibular joint. This mobile joint permits us to speak, eat, drink and laugh.

Structures of skull joints are:

• Plane- internasal structure
• Serrate- coronal structure
• Denticulate- lambdoid suture
• Squamous- parietotemporal suture

The anatomical position of the skull

The skull can be placed in proper orientation by considering any one of the two planes.

1. Reid's baseline is a horizontal line obtained by joining the infraorbital margin to the center of the external acoustic meatus, i.e. auricular point.
2. Frankfurt's horizontal plane of orientation is obtained by joining the infraorbital margin to the upper margin of the external acoustic meatus.

Methods of study of the skull

The skull can be studied as a whole. The whole skull can be studied from the outside or externally in different views:

• Superior view or norma venticalis.
• Posterior view or norma occipitalis.
• Anterior view or norma frontalis.
• Lateral view or norma lateralis.
• Inferior view or norma basalis.

The whole skull can be studied from the inside or internally after removing the roof of the calvaria or skull cap:

• Internal surface of the cranial vault.
• The internal surface of the cranial base shows a natural subdivision into anterior, middle, and posterior cranial fossae.

The skull can also be studied as individual bones. Mandible, maxilla, ethmoid and zygomatic, etc. 

Peculiarities of skull bone

1. The base of the skull is ossified in cartilage while the skull cap is ossified in a membrane.
2. Skull bones are united mostly by structures.
3. Skull has foramina for "emissary veins" which connect intracranial venous sinuses with extracranial veins. These try to relieve raised intracranial pressure. Infection may reach through the emissary's veins into cranial venous sinuses as these veins are valveless.
4. Skull lodges brain, meninges, CSF, glands like hypophysis cerebri and pineal, venous sinuses, teeth, special senses like the retina of eyeball, taste buds of the tongue, olfactory epithelium, cochlear and vestibular nerve endings.

Some skull bones have air cells in them and are called pneumatic bones, e.g. frontal, maxilla.

• They reduce the weight of the skull.
• They maintain the humidity of inspired air.
• They give resonance to voice.
• These may get infected resulting in sinusitis.