The syllabary systems of Japanese (hiragana and katakana) are examples of almost perfectly shallow orthographies—the kana correspond with almost perfect consistency to the spoken syllables, although with a few exceptions where symbols reflect historical or morphophonemic features: notably the use of ぢ "ji" and づ "zu" (rather than じ "ji" and ず "zu", their pronunciation in standard Tokyo dialect) when the character is a voicing of an underlying ち or つ (see rendaku), and the use of は, を, and へ to represent the sounds わ, お, and え, as relics of historical kana usage.