80. Pons – position, parts, external view, internal structure. The fourth ventricle.

PONS

• The pons is the largest part of the brainstem, situated above the medulla and below the midbrain
• Approximately 2.5 cm in the length
• Its name comes from the latin word for "bridge" as it serves as a connection both cerebellar hemispheres by middle cerebellar peduncle (MCP) on each side
• Its grey matter contains nuclei of the cranial nerves (V, VI, VII, VIII).

External Features:

• 1 Bulbopontine sulcus (sulcus bulbopontinus)
• marks the transition between the medulla oblongata and the pons
• n. VI emerges from the brainstem
• 2 Middle cerebellar peduncles (pedunculi cerebellares medii)
• connect the pons and cerebellum
• form the lateral borders of the pons
• contain the afferent pontocerebellar tracts
• 3 Rhomboid fossa (fossa rhomboidea)
• is on the dorsal surface of the pons
• together with the medulla oblongata, forms the floor of the fourth ventricle

• 4 Facial colliculus (colliculus facialis)
• a little eminence formed by the nucleus of the facial nerve and its fibres as they loop around the abducens nerve
• 5 Basilar sulcus (sulcus basilaris)
• a groove on the ventral surface of the pons containing the basilar artery
• 6 Pontocerebellar angle (angulus pontocerebellaris)
• contains the facial and vestibulocochlear nerves as they emerge from the brainstem
• 7 Trigeminofacial line (linea trigeminofacialis of Henle)
• an arbitrary borderline between nerves V and VII, which separates the pons from the cerebellum