Pons

The pons (Varolii) is the middle portion of the three parts of the brainstem, sitting above the medulla and below the midbrain. It acts as a relay between the cerebellum and cerebral hemispheres.

Gross anatomy

The pons has a bulbous shape and has two main components - the basis pontis (basal/ventral part) and the pontine tegmentum (dorsal part).

The basis pontis consists of white matter tracts (e.g. anterior and lateral corticospinal, corticobulbar and corticopontine tracts) with transverse fibers contributing to the bulk of the pons.

The pontine tegmentum is continuous with the tegmentum of the medulla and the midbrain. It contains multiple white matter tracts (e.g. medial longitudinal fasciculus, medial lemniscus, lateral lemniscus, etc) and grey matter nuclei (e.g. cranial nerve nuclei). Within the dorsal tegmentum lie four cranial nerve nuclei:

Posteriorly, the pons is connected to the cerebellum by the middle cerebellar peduncle. Inferiorly the posterior surface of the pons is slightly depressed, forming the diamond-shaped rhomboid fossa which is the floor of the fourth ventricle.

Relations

Blood supply

Primarily by vertebrobasilar circulation: