▁the ▁ca vern ous ▁sin us . ▁It ▁leaves ▁the ▁sk ull ▁through ▁the ▁for amen ▁rot und um , ▁where ▁it ▁becomes ▁more ▁cyl ind rical ▁in ▁form , ▁and ▁fir mer ▁in ▁texture . ▁After ▁leaving ▁for amen ▁rot und um ▁it ▁gives ▁two ▁branches ▁to ▁the ▁p ter yg op al at ine ▁gang l ion . ▁It ▁then ▁cross es ▁the ▁p ter yg op al at ine ▁f ossa , ▁incl ines ▁later al ward ▁on ▁the ▁back ▁of ▁the ▁max illa , ▁and ▁enters ▁the ▁orbit ▁through ▁the ▁inferior ▁orb ital ▁f iss ure . ▁It ▁then ▁runs ▁forward ▁on ▁the ▁floor ▁of ▁the ▁orbit , ▁at ▁first ▁in ▁the ▁inf ra orb ital ▁gro ove ▁and ▁then ▁in ▁the ▁inf ra orb ital ▁canal ▁remaining ▁outside ▁the ▁peri ost e um ▁of ▁the ▁orbit . ▁It ▁then ▁emer ges ▁on ▁the ▁face ▁through ▁the ▁inf ra orb ital ▁for amen ▁and ▁termin ates ▁by ▁div iding ▁into ▁inferior ▁pal pe br al , ▁later al ▁nas al ▁and ▁superior ▁lab ial ▁branches . ▁The ▁n erve ▁is ▁accompanied ▁by ▁the ▁inf ra orb ital ▁branch ▁of ▁( the ▁third ▁part ▁of ) ▁the ▁max ill ary ▁ar tery ▁and ▁the ▁accomp any ing ▁ve in . ▁ ▁Branch es ▁Its ▁branches ▁may ▁be ▁divided ▁into ▁four ▁groups , ▁depending ▁upon ▁where ▁they ▁branch ▁off : ▁in ▁the ▁c ran ium , ▁in ▁the ▁p ter yg op al at ine ▁f ossa , ▁in ▁the ▁inf