The cranial nerve nucleus, supplying the marked muscle with arrow, lies at the level of:
The marked muscle is medial rectus, which is supplied by occulomotor nucleus in the midbrain, at the level of superior colliculus. All extraocular muscles are supplied by 3rd cranial nerve (Occulomotor Nerve) except LR6SO4 (Lateral rectus by 6th cranial nerve and Superior Oblique by 4th cranial nerve)
Superior colliculus
Inferior colliculus
Facial colliculus
Olive
Pharynx, larynx and trachea and cranial nerves 3,4,6