Source : Webster's Revised Unabridged Dictionary (1913)

Longitudinally \Lon`gi*tu"di*nal*ly\, adv.
   In the direction of length.

Source : WordNet®

longitudinally
     adv 1: across time; "We studied the development of the children
            longitudinally"
     2: in the direction of the length; "He cut the paper
        lengthwise" [syn: {lengthways}, {lengthwise}, {longwise},
        {longways}]
     3: with respect to longitude; "longitudinally measured"