It is the superior colliculus here in the tectum. The nuclear mass just ventral to the aqueduct is that of the oculomotor nerve (III). You can see the lemnisci all crowded in the white outline, ready to jump up to the thalamus.

The distinct landmark in the tegmentum is the red nucleus. Note the 'shell' of fibres around it. Many of these fibres are on their way to the thalamus, having come from the deep nuclei (the dentate) of the cerebellum. The circuit from the cerebral cortex and back via the cerebellum is almost complete...

The substantia nigra and the fibre bundles of the cerebral peduncle need no further comment.

Hope you enjoyed this pictorial journey. Make sure you supplement it with theoretical questions at every stage!

Best wishes.