The semilunar ganglion of the trigeminal nerve lies deep within the skull. The three branches of the nerve leave through large separate openings in the base of the skull.
The trigeminal nerve is the 5th cranial nerve. Its three portions are the ophthalmic nerve controlling sensation to the upper face, the maxillary nerve controlling sensation to the mid-face, and the mandibular nerve supplying sensation to the lower face and the skin around and above the ear. Each of the branches supplies both soft tissue and bone.
All large ganglia in the body can harbor certain viruses. Oral herpes infections “hibernate” within the semilunar ganglion, traveling down the nerve roots to the mouth when the virus is activated by stress.