The uncus (on the medial aspect of the temporal lobe) herniates under the tentorium cerebelli. The uncus can compress the oculomotor nerve (CN III), compromising the parasympathetic fibers and resulting in ipsilateral pupillary dilation with associated ophthalmoplegia ("down and out"). Cheyne-Stokes respirations are commonly seen with mesial temporal transtentorial herniation. If the uncus is forced fuher medially, it compresses the cerebral peduncle, producing contralateral hemiparesis. After the brain herniates, the patients are decerebrate and comatose, have fixed and dilated pupils, and eye movements are absent. Ref: Cowan J.A., Thompson B. (2010). Chapter 36. Neurosurgery. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.