Hypoglossal Nerve

Description

Arising from multiple rootlets in the preolivary sulcus of the medulla oblongata, the hypoglossal nerve (cranial nerve XII) is shown emerging between the pyramid medially and the olive laterally, then gathering into a single trunk that courses anterolaterally toward the hypoglossal canal. Neighboring cranial nerves are represented in parallel, with the pontomedullary junction and lower pons superior to the medullary segment where CN XII originates. Superficial venous structures in blue track along the ventral brainstem, providing orientation against the red-coded midbrain, pons, and medulla. For teaching brainstem surface anatomy, this ventral medullary region is the cleanest place to anchor CN XII, because its rootlets line up predictably along the pyramid, just medial to the inferior olive, and sit close to corticospinal fibers that define the pyramidal tract. That relationship matters in clinical localization: a medial medullary infarct (often anterior spinal artery territory) can injure the hypoglossal fascicles and pyramid together, producing ipsilateral tongue weakness with contralateral hemiparesis. Tongue deviation toward the lesion on protrusion is the bedside clue. Short and memorable. Neuroanatomy and head and neck courses can use this figure to differentiate preolivary (hypoglossal) from postolivary (glossopharyngeal, vagus, accessory) rootlet exit zones, and to support captions in stroke localization chapters or cranial nerve examination guides. Surgical educators may also pair it with skull base material when discussing the hypoglossal canal and lateral approaches to the lower clivus and occipital condyle region. Anatomical accuracy verified by SciePro's Medical Advisory Board.