Medial recticular neurons projecting Rostrally.

1. In the latter part of investigations on the medial reticular neurons, stimulation was applied to the ipsilateral tegmental tract in the upper pontine level. Of the 426 neurons in this series, 56 had rostrally projecting axons as evidenced by their antidromic responses. 2. Of these 56 neurons, 41 were activated by limb nerve stimulation, usually very strongly, and so qualify as units in the reticular activating system. Fastigial stimulation monosynaptically excited 14 of these reticular activating neurons, so providing and ascending pathway from the cerebellar vermis. 3. Axonal branching has been demonstrated by antidromic testing in four reticular neurons with ascending axons. In two there were branches to the fastigial nucleus and in two, down the spinal cord. 4. The latency histograms of the excitatory and inhibitory responses resembled those for reticular neurons with descending axons except for the poverty of inhibitory responses in neurons not receiving a fastigial projection.