An ipsilateral CN III palsy with contralateral weakness and ataxia is a midbrain syndrome (Weber + Claude = Benedikt). The third nerve palsy is on the left and the limb signs are on the right, so the lesion is in the left midbrain.

• A right midbrain lesion would give a right CN III palsy.
• A hemispheric infarct does not cause a third nerve palsy.
• A pontine lesion affects CN VI/VII, not CN III.