The vastus lateralis site is used for infants less than 7 months old and people who are unable to walk or who have loss of muscular tone. The site is located by dividing the front thigh into thirds vertically and horizontally to form nine squares; the injection is administered in the outer middle square. This site is also the usual site of administration for epinephrine autoinjectors, which are used in the outer thigh, corresponding to the location of the vastus lateralis muscle.