Nucleus isthmi of the frog: structure and tecto-isthmic projection.

The morphology of neurons in the isthmic nucleus was studied with the Golgi technique. Most of the neurons have thick dendrites covered with lamelliform dendritic processes. The tecto-isthmic projection was investigated with the Fink--Heimer technique after partial tectal lesions. The anteromedial part of the tectum projects on the dorsal and anterior part, the caudomedial tectal region on the dorsal and posterior part of the nucleus. The posterolateral tectal area projects on the anterolateral part of the nucleus, and the axons originating in the anterolateral tectal quadrant terminate in its ventral and caudal part.