Anatomy is the study of the placement of structures within living things. This includes organs, muscles, bones, fibres, and everything else found within a body. It also studies the disorders and diseases associated with the physical body.
Modification artists must have a good knowledge of anatomy to determine how a body will react to a certain modification; for example, if a certain piercing will reject due to the composition of a client's ear cartilage, or whether a scarification could be dangerous on a client who has very thin blood (anaemia) or bleeds excessively when the skin is broken (haemophilia). Advanced piercings and procedures like clavicle and implants depend heavily on the piercer's knowledge of anatomy.
Clients should also have a working knowledge of anatomy since a working knowledge of anatomy helps with researching and discussing mods.
The most popular text (but not the only text) for studying anatomy is Gray's Anatomy. Gray's Anatomy is freely available on the web. Folio facsimiles of the original editions may be found for roughly $10. Researchers have also created tools compiled from images taken from donated bodies that were frozen and methodically sliced and photographed. Other recommended reading includes, "Essential Clinical Anatomy", by Agur & Moore.