In "Row, row, row your boat," the registral units (intervals) are ^1-^3, ^3-^5, ^8-^5 (expanded to ^8-^1), and ^5-^1. In "Frère Jacques," the sequence is ^1-^3, ^3-^5, ^5-^1, and ^1-^-5-^1. Any of these units that include ^1 or ^8 can act as the close. Here are some examples.
From Novello's School Round-Book, published in two volumes (1852, 1854). "Thou, poor bird" is a registral sibling of "Row, row, row your boat," the only difference being that the third unit stays on ^8-^5. If the end is taken with the fermatas (as suggested by the volumes' editor), then one easily imagine a singer repeating D5 for the second syllable of "warble."
In "The rose's age is but a day" from volume 2, the first three units are the same, but the fourth is restricted to a functional but non-melodic bass. There are no fermatas this time, but one can easily imagine four voices ending together, with the simple rising line in the uppermost register.
In "Go learn of the ant," also from volume 2, the harmonic vocabulary is a bit richer, and we can discern in the first unit the shape of an ascending Urlinie variant: ^5-^6-^8-^7-^8.
Three-voice rounds can easily dispense with the upper fourth—in fact, many do in the 19th-century collections I have examined to date—but a few are like "The rose's age is but a day." In "Come let us all a maying go," for example, the division of soprano, alto, bass is quite clear, and the soprano—after its descending octave in the first phrase—remains in the upper fourth for the second phrase.
This round from the New York Glee Book (1844) is similar in its basic design but manages to spread melodic values over the three parts.
Canons, catches, and rounds were very popular entertainments in earlier centuries, as well. Here are two from Thomas Ravenscroft's Pammelia (1609), which is subtitled "Musicks Miscellanie, or, a Mixed Varietie of Pleasant Roundelayes, and delightfull Catches." Note in "Dame lend me a loafe" that the ending (final unit) is in the upper fourth.
The first example was about food; the second is about drink. I have marked the three units and boxed their closing figures.
