Location and Formation
The jugular foramen is situated between the occipital and temporal bones. It connects the posterior cranial fossa to the external skull base and is visible on a macerated skull from the inferior (basal) view (norma basalis).
The foramen is formed by the apposition of two bone structures:
- Jugular notch (Incisura jugularis) — located on the outer margin of the lateral part of the occipital bone.
- Petrous part of the temporal bone.
Posterior to the jugular notch lies the jugular process (Processus jugularis). Anterior to it projects the intrajugular process (Processus intrajugularis), which divides the foramen into vascular and neural compartments.
Contents of the Jugular Foramen
The structures passing through the foramen belong to a unified "vagal system"—mixed cranial nerves that share common brainstem nuclei:
- Glossopharyngeal nerve (Nervus glossopharyngeus, CN IX) — exits the skull and passes between the internal carotid artery and the internal jugular vein toward the stylopharyngeus muscle.
- Vagus nerve (Nervus vagus, CN X) — exits the skull together with the accessory nerve.
- Accessory nerve (Nervus accessorius, CN XI) — its spinal roots initially ascend into the cranial cavity through the foramen magnum, join the cranial roots, and the combined trunk exits the skull via the jugular foramen. After exit, the spinal part forms the external branch, while the cranial part joins the vagus nerve.
- Meningeal branch of the vagus nerve — arises from the superior cervical ganglion, passes through the jugular foramen, and innervates the dura mater of the posterior cranial fossa.
- Posterior meningeal artery — enters the cranial cavity through the jugular foramen to supply the dura mater of the posterior cranial fossa.
Topography of Ganglia
Sensory ganglia of the cranial nerves traversing this region are located near the jugular foramen:
- Ganglia of the glossopharyngeal nerve — superior and inferior ganglia.
- Ganglia of the vagus nerve — superior (jugular) and inferior (nodose) ganglia.
Central processes of these sensory ganglion cells terminate in the sensory nucleus of the tractus solitarius (n. tractus solitarius).
Clinical Significance
Unilateral damage to the external branch of the accessory nerve after its exit from the jugular foramen causes flaccid paralysis of the entire sternocleidomastoid muscle and the upper part of the trapezius muscle.
To test the function of the accessory nerve, the patient is asked to turn or tilt the head and to shrug the shoulders against resistance applied by the examiner.