Starting in Early Middle Japanese, as more and more Chinese characters were borrowed into Japanese, the language acquired consonants fronted with glides. Those fronted with the palatal glide are described in the Y-row rule, but Early Middle Japanese also introduced consonants fronted with labial glides (i.e., CwV). These were far more limited in range than their palatal counterparts, however, affecting only the K- and G- rows. instead of , , and for the vowels of onset, like the palatal glides, the vowels of onset for the labial glides were , , and , and used the kana , , and ("wa", "wi", and "we"). Finally, while the palatal glides are written with an I-column kana, the labial glides are written with a U-column ( "U-dan") kana. However, when historical kana was standardized in the Meiji Period, only the syllables with historical were indicated. Nevertheless, some classical texts may indicate the other differences, and some resources will refer to them, so it is useful to be familiar with them. This rule applies exclusively to Sino-Japanese words. Some examples: