Fish (Pisces) typically have 10 pairs of cranial nerves (CN I–X), compared to the 12 pairs found in tetrapods (amphibians, reptiles, birds, mammals). Fish lack cranial nerves XI (accessory) and XII (hypoglossal), which evolved with the tetrapod body plan to serve neck muscles and tongue movements. The 10 cranial nerves of fish include olfactory (I), optic (II), oculomotor (III), trochlear (IV), trigeminal (V), abducens (VI), facial (VII), auditory (VIII), glossopharyngeal (IX), and vagus (X).