Anatomic studies on the superior colliculus.

The superior colliculus is organized into a superficial zone which is directly connected with other parts of the visual system and a deep zone which is not directly connected toith other visual centers. Within the superficial zone, there is a convergence of retinal and visual cortical afferents. The size, distribution, and synoptic patterns formed varies between animals. Removal of an eye in neonatal rats, at a time when there are few synapses formed in the colliculus, causes a great increase in the area of distribution of the uncrossed pathway of the remaining eye. At least some of the increased pathway arises from areas of retina which normally would have projected only contralaterally. Removal of an eye at later developmental stages results in no such abnormal projection, although there is evidence that synoptic sites formerly occupied by optic terminals became taken over by other neurons.