lon·gi·tu·di·nal 
(lŏn′jĭ-tdn-əl, -tyd-, lôn′-)
(lŏn′jĭ-tdn-əl, -tyd-, lôn′-)adj.
1.
a. Of or relating to longitude or length: a longitudinal reckoning by the navigator; made longitudinal measurements of the hull.
b. Concerned with the development of persons or groups over time: a longitudinal study of twins.
2. Placed or running lengthwise: longitudinal stripes.
lon′gi·tudi·nal·ly adv.