One Buddhist legend presents Guan Yin as vowing to never rest until she had freed all sentient beings from samsara, reincarnation. Despite strenuous effort, she realized that still many unhappy beings were yet to be saved. After struggling to comprehend the needs of so many, her head split into eleven pieces. Amitabha Buddha, seeing her plight, gave her eleven heads with which to hear the cries of the suffering. Upon hearing these cries and comprehending them, Avalokitesvara attempted to reach out to all those who needed aid, but found that her two arms shattered into pieces. Once more, Amitabha came to her aid and appointed her a thousand arms with which to aid the many. Many Himalayan versions of the tale include eight arms with which Avalokitesvara skillfully upholds the Dharma, each possessing its own particular implement, while more Chinese-specific versions give varying accounts of this number. (From: http://en.wikipedia.org/wiki/Kannon). Thank Noriko!