<?php

$array = array('1','2','3','4','5','6','7');
list($beginning, $ending) = array_chunk($array, ceil(count($array)/2));

var_dump($beginning);
var_dump($ending);

?>

array(4) {
  [0]=>
  string(1) "1"
  [1]=>
  string(1) "2"
  [2]=>
  string(1) "3"
  [3]=>
  string(1) "4"
}
array(3) {
  [0]=>
  string(1) "5"
  [1]=>
  string(1) "6"
  [2]=>
  string(1) "7"
}