As the facial nerve and nervus intermedius pass through the anterior superior quadrant of the internal acoustic meatus it enters the Fallopian canal, passing anterolaterally between and superior to the cochlea (anterior) and vestibule (posterior), and then runs back posteriorly at the geniculate ganglion (where the nervus intermedius joins the facial nerve and where fibers for taste synapse). It is here that three branches originate:

Greater superficial petrosal nerve

Lesser petrosal nerve

External petrosal nerve

The labyrinthine segment is the shortest only measuring 3-4 mm. It is also the narrowest and the most susceptible to vascular compromise.