Greater Petrosal Nerve
Figure 22. Cranial Nerve VII - Facial Nerve
The greater petrosal nerve is the first to branch within the temporal bone. It carries parasympathethic fibers out of the temporal bone through the hiatus of the greater petrosal nerve back into the middle cranial fossa. It then passes out of the cranium for good entering the foramen lacerum where it joins the deep petrosal nerve to become the nerve of the pterygoid canal. The deep petrosal carries postganglionic sympathetic fibers from spinal ganglia while the greater petrosal is mostly composed of pre-ganglionic parasympathetic fibers. This combined nerve of the pterygoid canal immediately enters the pterygoid canal in the sphenoid. After passing through the sphenoid the canal opens into the pterygopalatine fossa where the nerve enters the pterygopalatine ganglion which is associated with the maxillary nerve as mentioned in the earlier section. The parasympathetic fibers synapse in the ganglion and the post ganglionic fibers pass into the maxillary nerve along with post-ganglionic sympathetic fibers already traveling in the nerve. These fibers travel along the maxillary nerve to the zygomatic nerve. Finally, they travel through a communicating branch to the ophthalmic nerve which gives off the lacrimal nerve to the lacrimal gland.