The skull is the bony structure of the head, enclosing the brain and supporting the face. Head anatomy also includes the muscles, sensory organs, cavities, vessels and nerves arranged around it. Understanding these structures begins with separating the braincase from the facial skeleton and then tracing their relationships.
What bones form the skull?
The neurocranium is the part of the skull that surrounds the brain. The viscerocranium is the bony framework of the face. Most skull bones meet at sutures, joints held together by fibrous connective tissue rather than freely moving joint surfaces.
The bones of the neurocranium are:
- The frontal bone, which forms the forehead and contributes to the roofs of the eye sockets.
- The right parietal bone and left parietal bone, which form much of the roof and sides of the braincase.
- A temporal bone on each side, contributing to the sides and base of the skull and housing the organs of hearing and balance.
- The occipital bone, which forms the back and part of the base of the skull.
- The sphenoid bone, which lies centrally in the skull base and contributes to the eye sockets.
- The ethmoid, which contributes to the anterior skull base, nasal cavity and inner walls of the eye sockets.
The facial skeleton comprises the paired maxillae, zygomatic bones, nasal bones, lacrimal bones, palatine bones and inferior nasal conchae, together with the unpaired vomer and mandible. The zygomatic bones form the cheek prominences; the vomer forms part of the bony nasal septum, the partition between the nasal passages.
Each maxilla supports the upper teeth and contributes to the hard palate, the bony roof of the mouth. The mandible supports the lower teeth and moves at the temporomandibular joints, where it articulates with the temporal bones.
In the 3D model next to this article, you can rotate the skull and switch layers on and off to compare its overall shape from different directions.
What are the cranial cavity and cranial fossae?
The cranial cavity is the space enclosed by the neurocranium. It contains the brain, blood vessels and meninges, the protective membranes surrounding the brain. Its floor is divided into cranial fossae: broad depressions that support different brain regions.
| Cranial fossa | Main bones forming its floor | Main brain region supported |
|---|---|---|
| Anterior cranial fossa | Frontal bone, ethmoid and sphenoid bone | Frontal lobes, the anterior regions of the cerebral hemispheres |
| Middle cranial fossa | Sphenoid bone and temporal bones | Temporal lobes, the lower lateral regions of the cerebral hemispheres |
| Posterior cranial fossa | Mainly occipital bone and temporal bones | Cerebellum, pons and medulla, regions concerned with coordination and connections to the spinal cord |
The skull base contains foramina, openings through which nerves and vessels pass. The foramen magnum is the large opening in the occipital bone through which the lowest part of the brainstem continues as the spinal cord. The brainstem connects the larger brain regions with the spinal cord.
Which muscles move the face and jaw?
Muscles of facial expression usually attach to the skin as well as deeper tissues, allowing them to change facial shape. Orbicularis oculi closes the eyelids, orbicularis oris closes and shapes the lips, zygomaticus major raises the corner of the mouth, and zygomaticus minor raises the upper lip. Buccinator forms the muscular wall of the cheek and keeps food between the teeth during chewing.
Mastication means chewing. Its principal muscles are the masseter, temporalis, medial pterygoid and lateral pterygoid on each side. The left masseter, like its counterpart on the right, runs from the cheek arch to the mandible and elevates the jaw.
Temporalis is a broad, fan-shaped muscle on the side of the skull that elevates the mandible; its posterior fibres also retract it, drawing it backwards. The pterygoid muscles lie deep to the mandible: the medial pterygoid assists elevation, while the lateral pterygoid helps move the jaw forwards and open it. Alternating activity of the pterygoid muscles contributes to side-to-side movements.
What is inside the orbit?
An orbit is a bony socket containing an eye, its movement muscles, nerves, vessels and supporting fat. Its walls are formed by contributions from the frontal, sphenoid, zygomatic, maxillary, palatine, lacrimal and ethmoid bones. The orbit opens forwards, while passages at its back connect it with the cranial cavity.
The optic canal carries the optic nerve, which conveys visual information, and the ophthalmic artery. The superior orbital fissure, a slit between parts of the sphenoid bone, transmits nerves involved in eye movement and sensation.
The lacrimal gland produces tears and lies in the upper outer part of each orbit. Tears pass across the eye surface and drain towards the inner corner, then through small channels into the lacrimal sac. The nasolacrimal duct carries them from this sac into the nasal cavity.
How is the nasal cavity organised?
The nasal cavity extends from the nostrils to the choanae, the posterior openings into the upper throat. The nasal septum separates its right and left sides and consists of cartilage, a flexible supporting tissue, together with parts of the ethmoid and vomer.
Nasal conchae are curved bony shelves projecting from the lateral walls. The superior and middle conchae belong to the ethmoid, whereas the inferior nasal conchae are separate bones. The passages beneath these shelves are called meatuses; they receive openings from the tear-drainage pathway and nearby air-filled spaces.
The paranasal sinuses are air-filled cavities in the frontal, ethmoid, sphenoid and maxillary bones that communicate with the nasal cavity. Most of the cavity is lined by mucosa, a moist tissue lining that helps warm, humidify and filter inhaled air. Specialised smell-sensitive tissue lies high in the cavity.
What forms the oral cavity?
The oral cavity comprises the vestibule, the space between the lips or cheeks and the teeth, and the oral cavity proper, the space inside the dental arches. The hard palate forms its anterior roof; the soft palate forms the movable posterior roof. The soft palate rises during swallowing to help close the passage between the nasopharynx, the nasal part of the throat, and the oropharynx, the part behind the mouth.
The tongue occupies much of the oral cavity and rests on its muscular floor. Muscles within the tongue change its shape, while muscles connecting it to surrounding structures change its position. Together, these movements support chewing, swallowing and speech.
Salivary glands deliver saliva through ducts into the mouth. The parotid duct opens into the cheek-side vestibule, while the submandibular and sublingual glands drain into the floor of the mouth.
How do the carotid arteries supply the head?
The common carotid artery divides in the neck into external and internal carotid arteries. Arteries carry blood away from the heart; their branches distribute it to individual tissues. The external carotid artery supplies much of the face, scalp and deeper facial structures.
Important external carotid branches include the facial artery for the face, the superficial temporal artery for the scalp, and the maxillary artery for deep regions of the face. The lingual artery supplies the tongue and neighbouring tissues.
The internal carotid artery enters the skull through the carotid canal and contributes substantially to the brain's blood supply. Its ophthalmic branch supplies the orbit and also reaches parts of the forehead and nose. Vertebral arteries provide an additional route to the brain, so cerebral blood supply is not exclusively carotid.
What do the trigeminal and facial nerves do?
The trigeminal nerve is the main sensory nerve of the face, carrying information such as touch, pain and temperature. It has ophthalmic, maxillary and mandibular divisions. These supply broadly the forehead and upper face, middle face, and lower face respectively, with additional branches to deeper structures.
The mandibular division also carries motor fibres, nerve fibres that activate muscles, to the principal muscles of mastication. Its lingual branch carries general sensation from most of the anterior two-thirds of the tongue. Taste fibres from this region travel with the lingual nerve but belong to the facial nerve, not the trigeminal nerve.
The facial nerve supplies the muscles of facial expression. It also carries taste from most of the anterior two-thirds of the tongue and parasympathetic fibres, which stimulate secretion from certain glands. Taste from the vallate papillae, near the boundary with the posterior third of the tongue, is carried by the glossopharyngeal nerve. These parasympathetic fibres serve the lacrimal, submandibular and sublingual glands, distinguishing these functions from the trigeminal nerve's predominant role in facial sensation.