Regions of the head: face, cranial cavity and orbit
The head is conventionally divided into regions that include the face (hairline to chin), the cranial cavity (the space inside the skull) and the orbit (the bony eye socket).
Remember
The face is the front of the head from hairline to chin, the cranial cavity is the separate space inside the skull that holds the brain, and the orbit opens onto the face but is a region of its own.
Memory aid
The cranial cavity is the brain's own room, and the eye, ear and mouth each have a separate room of their own.
Use it to remember that the brain sits in its own compartment, apart from the eye, ear and mouth.
The head is conventionally divided into regions. A region is defined either by surface landmarks (such as the hairline) or by what it contains.
The face is the anterior (front) visible region of the head, bounded above by the hairline and below by the chin. It contains the muscles of facial expression and the muscles of mastication (the chewing muscles). It also holds the sensory territories (the parts of the face whose feeling each branch carries) of all three branches of the trigeminal nerve, the nerve that carries feeling from the face. A skin-deep cut in this front region, from hairline to chin, is therefore a facial injury rather than an injury to a deeper space.
The cranial cavity is the space inside the skull, the brain's own room. It holds the brain, its meningeal coverings (the meninges, the membranes that wrap the brain), the cerebrospinal fluid (the clear fluid that cushions the brain), the proximal parts of the cranial nerves (the parts nearest the brain) and the dural venous sinuses (channels that drain blood from the skull). Bleeding inside the skull around the brain is in this cavity, but that localises the region and does not name the type of haemorrhage. Being surrounded by skull bone does not make a structure part of the cavity: the cochlea (the hearing organ of the inner ear) lies in the ear.
The orbit is the pyramid-shaped bony socket of the eye. Its base opens forwards onto the face and its apex points backwards. It houses the eyeball, the extraocular muscles (the small muscles outside the eyeball that move it), the optic nerve and orbital fat, which cushions the eye and steadies those muscles. It opens onto the face, yet it is a separate region from it.
Key facts
- Face boundaries
- the hairline above and the chin below.
- Face contents
- the muscles of facial expression, the muscles of mastication and the sensory territories of all three branches of the trigeminal nerve.
- Cranial cavity contents
- the brain, its meninges, the cerebrospinal fluid, the proximal parts of the cranial nerves and the dural venous sinuses.
- Orbit shape
- a pyramid-shaped bony cavity whose base opens forwards onto the face and whose apex points backwards.
- Orbit contents
- the eyeball, the extraocular muscles, the optic nerve and orbital fat.
- Localising only
- knowing that a bleed is in the cranial cavity does not tell you which type of haemorrhage it is.
Exam traps
- A wound between the hairline and the chin is not in the occipital region (the region over the back of the skull), because the wound is on the anterior surface, which defines the face.
- The auricular region (the region around the external ear, on the side of the head) does not name the front surface from hairline to chin, which is the face.
- The cochlea and vestibular apparatus (the hearing and balance parts of the inner ear) do not lie in the cranial cavity just because skull bone encloses them, because the ear is a separate region from the compartment that holds the brain.
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