[TA] a large fiber bundle passing longitudinally through the central mesencephalic and pontine tegmentum, distinguished from adjacent longitudinal groups of fiber-fascicles of the reticular formation by a more compact composition. In transverse sections of the mesencephalon the bundle occupies a large triangular area lateral to the medial longitudinal fasciculus; farther caudally it expands anteriorly (ventralward) and finally passes over the lateral side of the (inferior) olivary nucleus, becoming part of the latter's fiber capsule. The bundle contains fibers from the mesencephalic tegmentum and regions surrounding the central gray substance descending to the olivary nucleus; it also includes numerous fibers ascending from the medullary, pontine, and mesencephalic reticular formation to the thalamus and subthalamus region. SYN: tractus tegmentalis centralis [TA], central tegmental fasciculus.