What is the meaning of 巻ノ + number next to a book?

Question

What is the meaning of 巻ノ + number next to a book?

I know that

• 巻 = volume
• ノ = ?
• 七十二　= 72

So it's Volume [?] 72

Answer 1

巻【まき】の七十二 is just a traditional way to say "Volume 72". Were it not a ninja manga, we would normally say （第）七十二[巻]【かん】.

の is the only way to connect a noun to another in Japanese. Unlike English, you cannot directly attach "with", "from", "by" and such to a noun unless via の. The の alone is thus the most ambiguous and versatile modifier with a lot of idiomatic usages. Here if literally interpreted, it would be "72 in volume" or "72 among volumes", which is a fixed way to indicate that it is the 72nd book in the series.

PS
Although the Japanese writing direction could be right-to-left in horizontal alignment, something like 二十七ノ巻 is hardly used as a volume number marker. ～の巻【まき】 would be usually the traditional format of title, that is, an explanation comes before の.

(an episode from the anime 忍者ハットリくん)

Answer 2

卷ノ(の)七十二 can be read in two ways. The first 二十七ノ卷, this is an old way reading Japanese letters from right to left. The second 卷ノ七十二, this is a new modern way reading them from left to right. Even as a native speaker of Japanese, I am a little perplexed, and have done a little search about his Manga. The answer is: 卷ノ七十二, meaning Vol. 72.