The leaf-shaped pinna of the external ear is broad with medial (rostral) and lateral (caudal) margins. The ear is moved by three sets of muscles (rostral, ventral, and caudal) that are innervated by branches of the facial nerve (cranial nerve VII). It is designed to localize and collect sound waves and transmit them to the tympanic membrane (eardrum). Carriage of the pinna is breed-specific in the dog but mostly upright in the cat. The foramen has been described as having the shape of a sitting duck on the highest axial cuts.The pinna, or auricle, is a highly visible structure. CTĬT appearance of the foramen depends upon the level and angulation of the scan. Therefore, the bony margin (and not the size) of the foramen should guide diagnostic evaluation. However, the normal foramen will always be well-corticated. The size of the normal jugular foramen is remarkably variable and asymmetrical. Sigmoid part: posterolateral, passes the sigmoid sinus Intrajugular part: between the venous compartments and around the intrajugular processes, passes the glossopharyngeal nerve (anterolateral) and vagus and accessory nerve complex (posteromedial) Petrosal part: anteromedial, passes the inferior petrosal sinus In this system, the foramen is divided into 3 parts, 2 venous and 1 neural 3,4: The vagus nerve yields an auricular branch ( Arnold nerve) via the mastoid canaliculus on the lateral wall of the foramen adjacent to the mastoid segment of the facial nerve. Jugular bulb: a venous expansion sitting in the jugular fossa, between the endocranial sigmoid sinus and the exocranial jugular vein The pars vascularis is the posterolateral portion of the jugular foramen and is larger than the smaller anteromedial portion termed the pars nervosa. The glossopharyngeal nerve yields a tympanic branch ( Jacobson nerve) which reaches and supplies the middle ear along with the inferior tympanic artery via the inferior tympanic canaliculus which is occasionally seen at CT in cross-section at the level of the caroticojugular spine. The inferior petrosal sinus drains the cavernous sinus and courses in the petro-occipital fissure adjacent to the clivus prior to its exit through the pars nervosa and subsequent drainage into the internal jugular vein beneath the foramen. The pars nervosa is the anteromedial portion of the jugular foramen and is smaller than the larger, posterolateral pars vascularis. This nomenclature is misleading because both compartments contain vascular and neural structures. Pars vascularis: posterolateral and larger The jugular foramen is commonly described in two parts, separated by a fibrous septum or a bony septum called the jugular spine (intrajugular processes on the opposing surfaces of the temporal and occipital bones): Gross anatomy Divisions: 2-part classification Ascending occipital and pharyngeal arteries are also located in this foramen 5. The jugular foramen is the cranial foramen located posterior to the carotid canal, formed by the petrous temporal bone and occipital bone where the sigmoid sinus and inferior petrosal sinus drain into the internal jugular vein and where cranial nerves IX–XI ( glossopharyngeal, vagus, and accessory) exit 5.
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