 Cranial nerve 5, or the trigeminal nerve, is the largest cranial nerve, and its three branches carry mainly sensory innervation from most regions of the head. V1 travels to the orbit, V2 to the tergopalatine fossa, and V3 to the infratemporal fossa. Along the way, sympathetic and parasympathetic fibers hop on to branches of 5 to get to their target tissues. Today, we will look specifically at the tergopalatine fossa. The tergopalatine fossa is like a roundabout. It's a major hub for the distribution of V2, the maxillary nerve. Parasympathetic and sympathetic fibers enter the fossa and then hop onto V2. Let's have a look at the details of the tergopalatine fossa in a board diagram. So this is the tergopalatine fossa, sitting between the tergoid process of the sphenoid bone and the maxillary bone. This keyhole-shaped structure is the hub for the distribution of V2. A number of foramina and fissures allow structures to enter and leave this space. Sensory information from the nasal cavities, orbits, oral cavity, and pharynx is carried into the fossa and back to the brain is V2, the maxillary nerve. The maxillary nerve exits the fossa through the foramen rotundum. Fibers join 5 in this fossa, just like in the traffic roundabout. Parasympathetic fibers from 7 enter the fossa and synapse in the tergopalatine ganglion. Postganglionic fibers hop onto all of the branches of the maxillary nerve to get to the glands in neighboring regions. Interestingly, parasympathetic fibers to the lacrimal gland leave the fossa on V2 and then hop onto V1 in the orbit. Sympathetic fibers from the superior cervical sympathetic ganglion at the base of the skull travel into the head with the internal carotid artery. These postganglionic sympathetic fibers leave the artery and travel into the fossa, where they also hop onto all branches of V2. Let's have a look at some of these features in a skull. This is a lateral view of the skull. When I remove the mandible and the zygomatic arch, you can clearly see the tergopalatine fossa here between the maxillary bone and the tergoid process of the sphenoid bone. As the fossa is magnified, you can see a number of foramina and fissures. Here is the tergomaxillary fissure, which communicates between the infertemporal fossa and the tergopalatine fossa. Here is the inferior orbital fissure, which goes to the orbit. If we look deep into the fossa, we can see the sphenopalatine foramen on the medial wall, which communicates with the nasal cavities. And right here is the palatine canal that goes to the oral cavity. If we abstract from the skull the sphenoid bone here and look at it from the front, we can see the foramen rotundum and the tergoid canal. The foramen rotundum carries V2 into the tergopalatine fossa, and the tergoid canal carries parasympathetics from 7 and sympathetic from the carotid plexus into the fossa.