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MEDLINE Indexing Online Training Course

Category A - Anatomy

Indexing Principles

This Category contains the terms for organs, regions, tissues, and cells from both humans and animals. It also includes terms for subcellular elements which can be used for all organisms.

Terms in Category A apply to both animals and humans. One tree, however, A13 contains only animal terms, such as GILLS and FEATHERS.

Indexing anatomical terms in animals

If the term is strictly an animal term, such as GILLS or FEATHERS, index it IM if it is a main point.

If the term can apply to either humans or animals:

  • For invertebrates: index the anatomical term NIM and the animal IM

Mouth parts of the mosquito
ANIMAL (check tag)

  • For vertebrates: index the anatomical term IM; the animal may be IM or NIM (see Category B indexing)

Liver of rats
ANIMAL (check tag)


Liver of elephants
ANIMAL (check tag)

Some restrictions and special instructions apply to certain anatomical terms. Extremities and the specific extremity terms are indexed differently depending upon the type of organism. These terms are also annotated with specific indexing instructions. Example: the elbow of the dog is indexed FORELIMB not ELBOW.

Check annotations with other anatomical terms for organism-specific instructions.

There are a wide variety of terms in this category. In many cases the specific anatomical term needed to index a concept is in MeSH. Always check for the most specific term.

Last Reviewed: January 14, 2015