html - how to make one div scrollable out of 2 or more div -

i have 3 div tags , want make 1 div (of 3) scrollable

i have tried overflow:"auto" in div want make scrollable , overflow:"hidden" in div tags don't want make scrollable. not working. should fix size of div following 2 div don't want make scrollable

<div class="span4" style="overflow:hidden"> ... <\div>

<div class="span4" style="overflow:hidden"> ... <\div>

and following div want make scrollable

<div class="span4" style="overflow:auto"> ... <\div>

try overflow: scroll or overflow-y: scroll explicit