A 40-year-old male presents with headache and diplopia for 6 months, accompanied by left-sided weakness. Examination reveals right ptosis, right pupil dilation with absent pupillary light reflex, left-sided muscle strength grade 3, increased muscle tone (hypertonia), hyperactive knee reflex, positive Babinski sign, shallow left nasolabial fold, and tongue deviation to the left. The lesion is localized to: