Comparative Alien Physiology was a medical textbook written by Leonard McCoy. It was of sufficient importance to be included in the medical library of the USS Voyager.
In 2374, Harry Kim downloaded the book, along with Gray's Anatomy and other seminal medical literature into his new EMH when The Doctor seemed unlikely to return from the Alpha Quadrant. Kim deemed it a "classic" medical text. (VOY: "Message in a Bottle")
In "Ashes to Ashes", Seven of Nine included time for study of this topic on the Borg children's activity schedule. While it was never expressly stated, this is likely the text they would have used.