Vesalius devotes one hundred and sixty-eight pages to the bones and cartilages, treating these structures with a thoroughness that amazed his contemporaries. He was the first author who correctly described the osseous system as a whole. In numerous instances Vesalius places himself in direct opposition to the opinions of Galen. He denied the existence of the intermaxillary bone in adults, and showed that the inferior maxilla does not consist of two pieces, as has been asserted by Galen. The seven bones of the sternum were reduced to three by Vesalius. He denied Galen’s statement that the bones of the symphysis pubis separate during parturition. He was the first anatomist to give an accurate description of the sphenoid bone. A small aperture at the root of the pterygoid process of the sphenoid bone is called _foramen Vesalii_. Vesalius proved the existence of marrow in the bones of the hand, which had been denied by Galen. In all respects, he wrote more intelligently of the bones than any anatomist who had preceded him. [Illustration: DEEP MUSCLES OF THE BACK BY VESALIUS (From the “Fabrica”, 1543. Reduced one-half)] [Illustration: PART OF THE FIRST TEXT-PAGE OF THE “FABRICA”] The Second Book Vesalius devotes one hundred and eighty-eight pages to a description of the ligaments and the muscles. This part of his treatise, while it contains a few errors and does not reach the high plane of the first book, is superior to any work of its kind that had preceded it. Vesalius was the first writer to describe the internal pterygoid muscle. He denied the existence of a general muscle of the skin, and stated that the intercostal muscles merely separate the ribs without expanding or contracting the thorax. He held the view that nerves and muscles do not stand in any relation of proportionate strength to one another, large nerves often being distributed to small muscles. He also held that the tendons are similar in structure to the ligaments. [Illustration: PLATE OF THE ARTERIAL TREE BY VESALIUS (From the “Fabrica”, 1543. Reduced one-half)] Vesalius’s plates of the superficial muscles are among the most beautiful that have ever appeared. They have been copied in practically all later treatises on anatomy, and have been used extensively by art-anatomists. His plates of the deeper muscles, while naturally not so pleasing to the eye, are wonderfully near accuracy. The different muscles are drawn to show function as well as structure. The Third Book