The skull was stuck in his palm. Shiva used it as the begging bowl. While coming to this place (Bikshandar kovil), Vishnu requested his consort Lakshmi to give alms to Shiva. Shiva's grail was filled by the alms and Lakshmi came to be known as Poornavalli (the one who filled the grail). She got rid of Shiva's hunger completely. Since Shiva came with a begging bowl and his hunger was entirely satisfied, he is known as Bikshandar.