human body to effectively observe each muscle in the body is laid out. Each illustration displays a deepening view of the human body which can be followed while dissecting a human body. Vesalius also mentions the instruments needed to perform a dissection. Here Vesalius begins to describe how Galen's anatomical descriptions do not match his own observations. In order to show respect to Galen, he suggests Galen's use of anatomical structure is in fact correct, but not for humans. He even continues to describe some of the structures in the way Galen would. Book 3: The Veins and Arteries, Book 4: The Nerves In Books 3 and 4, Vesalius describes the veins, arteries, and nerves as vessels, but notes their differing physical structure: veins and arteries contains a hollow channel, but nerves do not. Vesalius describes the route by which air travels through the lungs and the heart. He describes this process as "a tree whose trunks divide into branches and twigs". He also describes how the body contains four veins (the portal vein, the venae cavae, the artery-like vein [now understood as the Pulmonary Vein], and the umbilical vein) and two arteries (the aorta, and the vein-like artery [now understood as the Pulmonary Artery]) as being the main vessels which branch out into smaller veins and arteries. Vesalius lists some six hundred vessels in his tabulation of arteries, veins and nerves, but fails to mention the smaller vessels located in the hands and feet, the terminal vessels of the cutaneous nerves, or the vessels in the lungs and liver. Book 5: The Organs of Nutrition and Generation Vesalius gives detailed descriptions of the organs of nutrition, the urinary system, and the male and female reproductive systems. The alimentary and reproductive systems each make up about forty percent of this book, and the description of the renal system and the correct technique for dissecting it makes up the remainder. In the final chapter, the longest chapter of the entire collection, Vesalius gives detailed step-by-step instructions on how to dissect the abdominopelvic organs. In the first half of the book, Vesalius describes the peritoneum, the esophagus, the stomach, the omentum, the intestines and the mesentery. He then goes on to describe the liver, gallbladder, and the spleen. Finally, he describes the kidneys, the bladder, and the ureters. Vesalius was unfamiliar with the anatomy of pregnancy, which lead him to erroneously provide