Final answer:
The superior oblique muscle is innervated by the trochlear nerve (CN IV), situated in the orbit, and is involved in medial rotation of the eyeball.
Step-by-step explanation:
The muscle that is innervated by the trochlear nerve (CN IV) is the superior oblique. This muscle is located within the orbit and is responsible for rotating the eyeball medially, in a motion known as intorsion. The trochlear nerve is the fourth cranial nerve and it focuses on eye movements, particularly as the eyes track objects closer to the face.
The superior oblique muscle's tendon threads through a structure called the trochlea, which is a pulley-like piece of cartilage situated at the superior and nasal part of the eye's orbit, before inserting into the eyeball.