THE PATHWAYS OF THE TECTUM (ANTERIOR COLLICULUS) OF THE MIDBRAIN IN CATS*

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Abstract
In 22 adult cats, exptl. lesions were placed in various parts of the midbrain. After an 18 day interval, the C. N. S. was studied by the Marchi technique. From these studies, it was concluded that the tectum is connected with other parts of the brain stem by the following fiber systems: The stratum zonale consists of an efferent tecto-nigral system via tractus peduncularis transversus. The tecto-protuberantial fibers rise from the stratum zonale. Afferent optic (geniculate) fibers occupy the stratum opticum homolaterally and contralaterally. The stratum lemnisci has afferent fibers homolaterally as well as contralaterally. The latter enter via the intraquadrigeminal commissure. The commissure continues into the pulvinar and ventral thalamic nuclei. The most important connections are via the radii and Meynert''s decussation. These fibers cross the midline from the caudal end of the colliculus to its anterior end. The fibers enter the interstitial, the red nucleus, and the reticulated nuclei contralaterally, and the lateral reticulated nuclei homolaterally. The tecto-reticulated fibers are continued by fibers which take their course in the predorsal bundles[long dash]tegmento-bulbar fibers. The pulvinar sends fibers to the habenular ganglion as well as the deep medullary layer. The posterior commissure enters into the Darksche-witsch nucleus homolaterally, the tegmentum as well as the tectum via radii-like fibers. There is a tractus tecto-ha-benularis parallel to the fasciculus retroflexus.