Cut text after a number of characters and after the last point.

gistfile1.php

$text = "Vivamus sagittis lacus vel augue laoreet rutrum faucibus dolor auctor. Praesent commodo cursus magna, vel scelerisque nisl consectetur et. Nullam id dolor id nibh ultricies vehicula ut id elit. Donec id elit non mi porta gravida at eget metus.";

$split = strpos($text, '. ', 10)+1;

$text1 = wpautop(substr($text, 0, $split));

$text2 = wpautop(substr($text, $split));