Synonyms can be in English or Latin and appear as spelled in the source. The NeuroNames Hierarchy is based on morphologic homology with the combination of substructures included in a given superstructure based on proximity. These criteria underlie the classical neuroanatomical classification of brain structures and, of course, do not necessarily imply homology based on other criteria, such as connectivity, function or ontogeny. While they represent legitimate neuroanatomical entities, they are not necessary elements of the minimal and exhaustive set of mutually exclusive structures required to describe the primate brain. Thus, they are described separately from the Hierarchy.
Ancillary terms fall into several major categories.
Almost half represent alternate ways of subdividing the brain. Many others sound as though they might be in the brain, but refer to structures outside the brain, e.g., in the spinal cord. Another group consists of terms referring to fiber pathways that are not readily distinguishable in myelin-stained sections. Other categories include terms based on cytoarchitectural, myeloarchitectural or embryological characteristics. Some terms referring to structures or areas defined by functional characteristics or by connectivity are also included as ancillary terms.