The affix ghañ comes after the root grah 'to seize' in composition with pari when it relates to sacrificial subjects.,
As उत्तरपरिग्राहः 'the northern fencing of the sacrificial altar'; अधरपरिग्राहः 'the southern fencing of the sacrificial altar'.
Why do we say 'when relating to sacrifices'? Observe परिग्रहः देवदत्तस्य 'the fencing of Devadatta'.,