How many skull bones are there

The sphenoid bone is divided into several parts: the body of the bone, two greater wings, two lesser wings, and the pterygoid processes. The sphenoid bone is one of the most complex in the body due to its interactions with numerous facial bones, ligaments, and muscles. The body that forms the middle of the sphenoid bone articulates with the ethmoid and occipital bone and forms a key part of the nasal cavity; it also contains the sphenoidal sinuses.

The greater wings form the floor of the middle cranial fossa that houses the frontal lobes and pituitary gland, and also the posterior wall of the orbit. The lesser wings project laterally and form the floor of the anterior cranial fossa and the superior orbital fissure through which several key optical nerves pass.

The ethmoid bone is a small bone in the skull that separates the nasal cavity from the brain. It is lightweight due to its spongy, air-filled construction and is located at the roof of the nose and between the two orbits.

The ethmoid bone forms the medial wall of the orbit, the roof of the nasal cavity, and due to its central location it articulates with numerous bones of the viscerocranium. Inside the neurocranium it articulates with the frontal and sphenoid bones. The frontal bone borders two other neurocranial bones—the parietal bones through the coronal sutures and the sphenoid bone through the sphenofrontal suture.

It also articulates with the zygomatic and nasal bones and the maxilla. Learning Objectives Differentiate the bones of the neurocranium. Anatomy and function. Diagram of cranial bones. Cranial bone conditions. Tips for healthy cranial bones. Read this next. The 12 Cranial Nerves. Medically reviewed by Deborah Weatherspoon, Ph.

Cranial CT Scan. What Is a Craniectomy? Medically reviewed by Alana Biggers, M. The joint between the mandible and the cranium, known as the temporomandibular joint, forms the only non-sutured joint in the skull. Most sutures are named for the bones that they articulate. At birth, many of the bones of the skull remain unfused to the soft spots described as fontanelle.

The bones fuse relatively rapidly through a process known as craniosynotosis, although the relative positions of the bones can continue to change through life.

In old age the cranial sutures may ossify completely, reducing the amount of elasticity present in the skull. As such, the degree of ossification can be a useful tool in determining age postmortem. Lateral view of a skull showing sutures : The dotted red lines indicate the location of skull sutures.

The paranasal sinuses four, paired, air-filled spaces surround the nasal cavity, and are located above and between the eyes, and behind the ethmoids. Skull Sinuses : This image shows the position of the sinuses in the human skull. Paranasal sinuses are a group of four, paired, air-filled spaces that surround the nasal cavity maxillary sinuses , above the eyes frontal sinuses , between the eyes ethmoid sinuses , and behind the eyes sphenoid sinuses.

The sinuses are named for the facial bones that they are located behind. The paranasal sinuses form developmentally through excavation of bone by air-filled sacs pneumatic diverticula from the nasal cavity.

The biological role of the sinuses is debated, but a number of possible functions have been proposed. These include:.

Superior view of infant skull : This image shows the location of the anterior frontal and posterior fontanelles. The ossification of the bones of the skull causes the fontanelles to close over a period of 18 to 24 months; they eventually form the sutures of the neurocranium.

The cranium of a newborn consists of five main bones: two frontal bones, two parietal bones, and one occipital bone. These are joined by fibrous sutures that allow movement that facilitates childbirth and brain growth.

At birth, the skull features a small posterior fontanelle an open area covered by a tough membrane where the two parietal bones adjoin the occipital bone at the lambda. This is called intramembranous ossification. The mesenchymal connective tissue turns into bone tissue. The much larger, diamond-shaped anterior fontanelle—where the two frontal and two parietal bones join—generally remains open until a child is about two years old.

The anterior fontanelle is useful clinically, as examination of an infant includes palpating the anterior fontanelle. Two smaller fontanelles are located on each side of the head. The more anterior one is the sphenoidal between the sphenoid, parietal, temporal, and frontal bones , while the more posterior one is the mastoid between the temporal, occipital, and parietal bones.

Lateral view of infant skull : This image show the location of the sphenoidal and mastoid fontanelles. The fontanelle may pulsate. Although the precise cause of this is not known, it is perfectly normal and seems to echo the heartbeat, perhaps via the arterial pulse within the brain vasculature, or in the meninges. This pulsating action is how the soft spot got its name: fontanelle means little fountain.

Parents may worry that their infant may be more prone to injury at the fontanelles. In fact, although they may colloquially be called soft spots, the membrane covering the fontanelles is extremely tough and difficult to penetrate. The fontanelles allow the infant brain to be imaged using ultrasonography.

Once they are closed, most of the brain is inaccessible to ultrasound imaging because the bony skull presents an acoustic barrier. Privacy Policy. Skip to main content. Skeletal System: Parts of the Skeleton. Search for:. The Skull. General Features and Functions of the Skull The human skull is the part of the skeleton that supports the structures of the face and forms a cavity for the brain.

Learning Objectives Describe the parts of the skull. Key Takeaways Key Points The adult human skull consists of two regions of different embryological origins: the neurocranium and the viscerocranium. The neurocranium is a protective shell surrounding the brain and brain stem.

The viscerocranium or facial skeleton is formed by the bones supporting the face. The bones that form the mouth and jaw are the two palatine bones, two maxilla bones, and the mandible. The two palatine bones form the roof of the mouth and help to form the mouth cavity. The two maxilla bones, one on the left and one on the right, form the top jaw and anchor our upper teeth.