By Elizabeth A. Murray, Mount St. Joseph University
There are many skull landmarks. Some are only found inside the skull, while others are on its surface, or connect through and through. There are also plenty of muscle attachments sites—some to anchor muscles of facial expression and others for muscles that move the head and neck. However, there are some which assume significance when we focus on movement and nerve supply. Which ones are those?
The Foramina
When it comes to skull landmarks, there are numerous foramina that provide entrance and exit for nerves and blood vessels.
Starting externally, with the ones that have some of the major openings, we begin with the supraorbital foramen or notch. It is situated just above each eye orbit. In some people it’s a foramen, and in others, just a notch in the edge of the orbit roof. Below each orbit are corresponding infraorbital foramina, satisfying the rule of adjectives.
Meatus
In vertical alignment with the infraorbital foramina are a pair of mental foramina in the mandible. This series of three bilateral openings transmits three paired branches of the fifth cranial nerve called the trigeminal nerve, and their corresponding veins and arteries. These nerves are responsible for sensations from the facial skin.
The eye orbits contain several openings; the optic canal that transmits our optic nerve, which is the cranial nerve of vision; as well as a small artery that supplies structures in the orbit. There are also superior and inferior orbital fissures that transmit branches of other cranial nerves, including the motor nerves that supply muscles that move the eyeballs around.
Progressing laterally, there is an external auditory meatus on each side of the skull. A meatus is a tube-like passage in a bone; this is lined with skin and transmits sound waves into the eardrum. Posteriorly is the largest foramen in the skull—the foramen magnum—which is Latin for ‘big hole’.
Foramen magnum transmits the brain stem, where it becomes the spinal cord, and also allows entrance of the vertebral arteries that ascend the neck through the transverse foramina of cervical vertebrae. On either side of foramen magnum are the occipital condyles that articulate with the first cervical vertebra.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
The Base of the Skull
There are many other openings at the base of the skull. Several of these openings transmit cranial nerves that provide sensation and motor control to structures mostly in the head and neck. Other passages are routes for blood vessels that need to enter the cranium, like the internal carotid arteries that work with the vertebral arteries to supply the brain. Some openings also transmit veins, like the internal jugular veins that leave the skull, leading blood low in oxygen away from the brain.
With the skullcap removed, we can see that there are just as many openings inside the skull. These passages are also the means by which nerves and vessels communicate between the head and neck or relay our special senses. Several pairs of cranial nerves are devoted to the special senses, which include sight, smell, taste, hearing, and equilibrium. Equilibrium is our special sense of balance maintenance, housed in the inner ear along with the sense of hearing.
There are five special senses, but touch is not one of them. Touch is a general sense, since general senses are found all over the body, and have relatively simple receptors, while special senses have complicated receptors, all of which are located in the head.
The Occipital Bone
At the posterior aspect of the skull are nuchal lines on the occipital bone; these are the attachment sites for some true back muscles in the neck. Behind each ear, one can feel the bumps created by our mastoid processes, and there are styloid processes just medial to them.
These landmarks are both on our temporal bones and are attachment sites for muscles of the neck. Two other bony landmarks at the base of the skull are the medial and lateral pterygoid plates of the sphenoid bone.
P-t-e-r means ‘wing’, as in the winged dinosaurs called pterodactyls. These pterygoid plates are attachments sites for muscles that help move the jaw. Laterally, the zygomatic arch—a bridge made partly of the zygomatic bone and partly by the temporal bone—can be easily felt passing posteriorly from the cheekbone. Laterally on the cranium, temporal lines stretch from the frontal bone to the parietal bone. The zygomatic arch and temporal lines are the origins for two major muscles of chewing.
The Mandible
The mandible has many bony landmarks, including for the insertions of the muscles that move it: the main portion of the jaw is the mandibular body, and the chin is called the mental protuberance. The angle of the jaw is located posteriorly, and the mandible’s ramus projects superiorly to terminate in the coronoid process anteriorly and the mandibular condyle posteriorly. The condyle is also known as the head of the mandible, and just inferior to it is a constricted neck.
The mandibular condyle articulates with the mandibular fossa on the temporal bone. This forms the only moveable joint of the skull, the temporomandibular joint, more commonly called the TMJ.
Common Questions about the Different Skull Landmarks
The eye orbits contain several openings; the optic canal that transmits our optic nerve, which is the cranial nerve of vision; as well as a small artery that supplies structures in the orbit.
A meatus is a tube-like passage in a bone; this is lined with skin and transmits sound waves into the eardrum.
Laterally on the cranium, temporal lines stretch from the frontal bone to the parietal bone. The zygomatic arch and temporal lines are the origins for two major muscles of chewing.
