Definition of COUNTERBORE. : to form a counterbore in: enlarge (part of a hole) by means of a counterbore.ADVERTISEMENT.efinition of COUNTERBORE. 1. : a flat-bottomed enlargement of the mouth of a cylindrical bore. 2. : a drill for making a counterbore â compare countersink.
The vestibulocochlear nerve (auditory vestibular nerve) , known as the eighth cranial nerve, transmits sound and equilibrium (balance) information from the inner ear to the brain.
The accessory nerve (cranial nerve XI) controls the sternocleidomastoid and trapezius muscles of the shoulder and neck. It begins in the central nervous system (CNS) and exits the cranium through a foramen. Unlike the other 11 cranial nerves, the accessory nerve begins outside the skull.