Projection fibers from the main sensory trigeminal nucleus and the supratrigeminal region

Fiber projections from the main sensory trigeminal nucleus and the supratrigeminal region (reticular formation dorsal and rostrodorsal to the motor trigeminal nucleus) in the cat and monkey have been studied by the Nauta, Fink‐Heimer and Marchi methods. Following experimental lesions in the main sensory trigeminal nucleus and its vicinity, the crossed ventral and the uncrossed dorsal trigeminal tracts were traced rostrally to the posteromedial ventral nucleus of the thalamus. The uncrossed dorsal trigeminal tract ascended through Forel's tegmental fascicle (tractus fasciculorum tegmenti Foreli). However, Forel's tegmental fascicle was composed mainly of the ascending reticular fibers terminating in the intralaminar nuclei of the thalamus and in the subthalamus. Commissural components distributing chidfly to the motor trigeminal nucleus of the opposite side appeared to arise from the supratrigeminal region as well as from the main sensory trigeminal nucleus. A fiber bundle, arising from the reticular zones surrounding the motor trigeminal nucleus, descended through the lateral reticular formation immediately ventromedial to the spinal trigeminal nucleus down to lower levels of the medulla oblongata. The functional significance of the supratrigeminal region as an interneuron system intercalated between the trigeminal sensory and the cranial motor systems is discussed.