"The Raven" has two distinct rhyme schemes, internal and external, which are ABCBBB and AABCCCCBCBB. These rhyme schemes are based on the first six lines of the poem and the same pattern of schemes is repeated throughout the poem.
Internal rhyme schemes are those that have rhyming words within the same line of the poem, while external rhyme schemes have a pattern of rhyming words at the end of the lines. For example, in the first line of "The Raven," "Once upon a midnight dreary, while I pondered weak and weary," the words "dreary" and "weary" rhyme with each other within the same line representing an internal rhyming pattern. On the other hand, in the second and fourth lines of the poem, "Over many a quaint and curious volume of forgotten lore" and "As of some one gently rapping, rapping at my chamber door," the words "lore" and "door" at the end of the lines rhyme with each other, representing an external rhyming pattern.