Single, etc., rhyme.
36. Rhyme is either single (on the last syllable only), double (on the two last), or triple (on the three last). Beyond three the effect would be burlesque, and this is hard to keep out of triple rhyme, and even sometimes seems to menace the double.
Fullness of sound.
37. In serious poetry the fuller in sound the single rhyme is the better.
Internal rhyme permissible,
38. Rhyme is usually at the end of the line; but it may be "internal"; that is to say, syllables at one or even more than one place within the line may rhyme to the syllable at the end or to each other, and syllables within one line may rhyme to those at corresponding places within another.
but sometimes dangerous.
39. But this has a dangerous tendency to break the lines up.
§ G. Miscellaneous
Vowel-music.