| Abstract: | We have correlated the tectal connections and cytoarchitecture of regions in the rabbit's midbrain and caudal thalamus. The inferior colliculus projects ipsilaterally to the central gray, superior colliculus, and via the brachium of the inferior colliculus to its interstitial nucleus and the parabrachial region of the midbrain tegmentum. From the brachium, fibers fan out to the principal and internal divisions of the medial geniculate. A smaller contralateral pathway sweeps into the contralateral inferior colliculus and in its brachium to the interstitial nucleus, the parabrachial region, and the internal and principal divisions of the medial geniculate. The superior collicular projection is mainly ipsilateral. Medially, fibers terminate in the central gray and pretectal area. Laterally, fibers ascend in the superior brachium to parabrachial region, suprageniculate pretectal nucleus, posterior complex, caudodorsal internal division of the medial geniculate, and to a discrete part of the ventral nucleus of later geniculate. A component of the commissure of Gudden originates in the rostral superior colliculus and terminates in the contralateral ventral lateral geniculate, posterior complex, pretectal area and midbrain tegmentum. Interconnections between the colliculi and overlap of their projections in the parabrachial region, the central gray, and the internal division of the medial geniculate are described. |
