Gray's Anatomy is a British anatomy textbook, originally developed by physician Henry Gray in the middle of the 19th century. It is still the most authoritative work of its kind, and is currently in its 40th edition, which was published in 2008.
Anatomy textbooks were available in the mid 19th century, but Gray took pains to make his textbook as inexpensive as possible. Due to its overwhelming popularity, successive editors took pains to make it as authoritative and complete as possible. However, this made the text more expensive and more unwieldy and, by the 35th edition, the book was too large, costly and complicated to be used by its original primary market - medical students. Since then, efforts have been made to streamline the work, and about 500 pages were lost between the 38th and 40th editions.
A separate American edition of the text went through 25 editions, but has not been published since 1990.
Many editions of the book are in the public domain and are widely available on the web. However, these are largely out of date as the understanding of human anatomy became increasingly sophisticated after 1950.