TA2Viewer: A web-based browser for 
INTRODUCTION Anatomical nomenclature is a powerful and unifying tool useful across broad swaths of biomedical activities. In clinical practice, consistent anatomical nomenclature allows physicians from different institutions, disciplines, and countries to work together. In education, it enables medical students to learn both from their mentors and from a variety of authoritative texts, and then apply that knowledge throughout their medical careers. In the computational domain, anatomical nomenclature provides semantic meaning to data—be it textual, tabular, or imaging—in a way that maximizes the potential for reusability and aggregation while reducing the possibility of ambiguity or error. At a time when the demand for worldwide medical education is growing and artificial intelligence (machine learning) algorithms are being used to process ever larger cohorts of biomedical data, there is an urgent need to develop digital anatomical nomenclatures that are accurate and intuitive to use, are aligned strongly with current medical usage, and are conveniently available to as many people and for as many applications as possible. This paper describes TA2Viewer, an online web-based application, anatomy knowledge base, and digital cross-referencing tool . TA2Viewer is designed to provide access to anatomical nomenclature and medical information to a worldwide community. It offers usability features not found in other online term browsers, including a multilingual interface and interactive search and browsing. TA2Viewer is based on the second edition of Terminologia Anatomica (TA2), the international standard anatomical nomenclature. It provides convenient access to all the information about the thousands of anatomical terms defined in TA2. The application includes multilingual search capabilities for finding terms efficiently and a hierarchy view that provides a relational context between different terms. Finally, TA2Viewer uses TA2 terms to cross-reference or search other sources of online medical knowledge. This extensible capability allows TA2Viewer to serve as a convenient term-based browser for online medical information. It is available for free at https://ta2viewer.openanatomy.org . The need for such a digital anatomical nomenclature resource was identified by the Open Anatomy Project at Brigham and Women’s Hospital in Boston ( https://openanatomy.org ) to facilitate and encourage accurate labeling of anatomical structures extracted from imaging data. The mission of the Open Anatomy Project is to deliver free and open online medical knowledge to the worldwide community. In particular, the Open Anatomy Project works with members of the medical and computer science communities to develop open digital anatomy atlases  using software tools such as 3D Slicer, an open source, freely available medical image analysis, and visualization platform . These digital atlases are created by manual or automatic segmentation of magnetic resonance or computed tomography (CT) imaging data of human subjects to extract anatomical structures. These structures must then be labeled accurately with anatomical terms for identification and education purposes. In our general experience, members of the interdisciplinary teams that build these atlases have “limited good intentions” about choosing accurate labels for atlas structures. They somewhat understand the importance of labeling and they prefer to assign accurate names rather than missing or inaccurate ones, but the “threshold of effort” they will expend to identify the correct label for a structure is not particularly high. In particular, data scientists with little exposure to formal anatomy education, including Latin anatomical terminology, depend heavily on easily accessible terminology references and lists. Without such convenient resources, there is often ad hoc labeling of structures using best guesses. Atlases lose much of their value as pedagogical or reference resources when they are labeled inconsistently or incorrectly. It is therefore worth significant effort to make accurate anatomical labeling as easy and convenient as possible. 

CHOOSING AN ANATOMICAL NOMENCLATURE We examined a range of available terminologies and ontologies when choosing which nomenclature to be the primary basis of our data labeling effort. Several qualities proved to be important. First, the nomenclature should be intuitive to our clinical collaborators based on their medical knowledge. Second, the terms and term organization should reflect human anatomy as understood by physicians, rather than on the basis of a more complex formal ontological organization. From a functional standpoint, a focused and well-organized nomenclature is preferable to larger, more complex, or less vetted ones, including multispecies ontologies in which appropriate terms are more difficult to locate. The nomenclature should ideally be under active development and vetted by a group of experts. Finally, its terms must be freely usable and redistributable without onerous licensing terms or other limitations on use. 2.1 | Existing digital resources Several existing digital nomenclatures and ontologies were evaluated using the foregoing criteria, including the Functional Model of Anatomy (FMA; http://fma.si.washington.edu/browser ), Uber Anatomy Ontology (UBERON; https://wwww.ebi.ac.uk/ols4/ontologies/uberon ), Unified Medical Language System (UMLS; https://uts.nlm.nih.gov/uts/umls ), and Medical Subject Headings (MESH; https://meshb.nlm.nih.gov ) and Systematized Nomenclature of Medicine—Clinical Terms (SNOMED-CT; https://browser.ihtsdotools.org ). Each of these nomenclatures failed at least one of our criteria. UBERON, for instance, is specifically designed to include multiple animal species , which makes it more suitable for comparative anatomy than human anatomy. UMLS  and SNOMED-CT  have significant limitations regarding open access and use. In addition, each of the online term browsers offered by the respective nomenclatures had their own deficiencies, including slow interactive search performance, a high level of visual complexity, or the need for a user account. Few, if any, offered user interfaces or terminology in languages other than English. 2.2 | Terminologia Anatomica As the result of this search, the Open Anatomy Project identified Terminologia Anatomica as the most appropriate nomenclature for general labeling of human anatomical structures. The second edition of Terminologia Anatomica (TA2) represents the latest revision of the standard nomenclature of human anatomy . Unlike other biomedical nomenclatures, controlled vocabularies, and ontologies such as FMA, UBERON, UMLS, and MeSH, TA2 is primarily useful for anatomists and physicians rather than ontologists. For instance, widely used biomedical reference works such as the Netter Atlas of Human Anatomy , Gray’s Anatomy , and Dorland’s Medical Dictionary , are aligned with TA2. This quality makes TA2 a useful foundation for medical software and online medical reference tools. Following the publication of Terminologia Embryologica by the Federative International Programme for Anatomical Terminology , the International Federation of Associations of Anatomists (IFAA) decided to publish future anatomical terminologies as open-access documents, abandoning its previous practice of publishing the international standard nomenclature in copyrighted book form to encourage its dissemination and use. When the second edition of Terminologia Anatomica (TA2) was ready for publication, FIPAT’s secretary for informatics (P.E.N.) was directed to publish it as a PDF under a CC-BY-ND license and as an online searchable database. During the publication process, the Open Anatomy Project approached the FIPAT secretary with a proposal to create an online representation of TA2, which is now TA2Viewer, that could be developed and used freely owing to the change of license. As the proposal met its objectives, the IFAA Executive Committee approved the collaboration. Prior to the publication of TA2, the first edition of Terminologia Anatomica  was the international standard human anatomical nomenclature. Generally, biomedical ontologies have not used TA or TA2 terms as their preferred anatomical terms. TA and TA2, like their predecessors ( Nomina Anatomica ), are structured lists of anatomical terms that are familiar and useful to anatomists, physicians, medical researchers, and medical students. A few anatomical websites purport to present Terminologia Anatomica , sometimes with TA’s hierarchy of terms (which could be a copyright infringement), sometimes with unauthorized revisions of TA terms, and sometimes as a searchable database of TA terms, which should be considered, like those in TA2, to be in the public domain. It was an explicit goal of the TA2Viewer collaboration to deliver a high-quality terminology viewer application that avoids diverging development and remains true to the new TA2 standard. TA2 provides an excellent foundation for labeling anatomical structures (even accepting that some structures, such as pathology or specialized anatomy, are not always within the scope of TA2). Once the Open Anatomy Project decided to adopt TA2 for labeling structures in images and reconstructions, the objective of TA2Viewer was broadened to providing users with access to a high-quality anatomical nomenclature using a convenient online tool, and then broadened again to providing information about anatomical terms and structures beyond those strictly available in TA2, such as equivalent terms in other languages, PubMed searches, links to other online biomedical resources, and collections of copyright-free images. In addition to pedagogical use, this extra information provides the user with greater confidence in labeling; for instance, when choosing between two closely related terms. By using TA2 as a common reference nomenclature for anatomy, TA2Viewer serves as a convenient and dynamic index for the fragmented world of biomedical terminology. 

Existing digital resources Several existing digital nomenclatures and ontologies were evaluated using the foregoing criteria, including the Functional Model of Anatomy (FMA; http://fma.si.washington.edu/browser ), Uber Anatomy Ontology (UBERON; https://wwww.ebi.ac.uk/ols4/ontologies/uberon ), Unified Medical Language System (UMLS; https://uts.nlm.nih.gov/uts/umls ), and Medical Subject Headings (MESH; https://meshb.nlm.nih.gov ) and Systematized Nomenclature of Medicine—Clinical Terms (SNOMED-CT; https://browser.ihtsdotools.org ). Each of these nomenclatures failed at least one of our criteria. UBERON, for instance, is specifically designed to include multiple animal species , which makes it more suitable for comparative anatomy than human anatomy. UMLS  and SNOMED-CT  have significant limitations regarding open access and use. In addition, each of the online term browsers offered by the respective nomenclatures had their own deficiencies, including slow interactive search performance, a high level of visual complexity, or the need for a user account. Few, if any, offered user interfaces or terminology in languages other than English. 

Terminologia Anatomica As the result of this search, the Open Anatomy Project identified Terminologia Anatomica as the most appropriate nomenclature for general labeling of human anatomical structures. The second edition of Terminologia Anatomica (TA2) represents the latest revision of the standard nomenclature of human anatomy . Unlike other biomedical nomenclatures, controlled vocabularies, and ontologies such as FMA, UBERON, UMLS, and MeSH, TA2 is primarily useful for anatomists and physicians rather than ontologists. For instance, widely used biomedical reference works such as the Netter Atlas of Human Anatomy , Gray’s Anatomy , and Dorland’s Medical Dictionary , are aligned with TA2. This quality makes TA2 a useful foundation for medical software and online medical reference tools. Following the publication of Terminologia Embryologica by the Federative International Programme for Anatomical Terminology , the International Federation of Associations of Anatomists (IFAA) decided to publish future anatomical terminologies as open-access documents, abandoning its previous practice of publishing the international standard nomenclature in copyrighted book form to encourage its dissemination and use. When the second edition of Terminologia Anatomica (TA2) was ready for publication, FIPAT’s secretary for informatics (P.E.N.) was directed to publish it as a PDF under a CC-BY-ND license and as an online searchable database. During the publication process, the Open Anatomy Project approached the FIPAT secretary with a proposal to create an online representation of TA2, which is now TA2Viewer, that could be developed and used freely owing to the change of license. As the proposal met its objectives, the IFAA Executive Committee approved the collaboration. Prior to the publication of TA2, the first edition of Terminologia Anatomica  was the international standard human anatomical nomenclature. Generally, biomedical ontologies have not used TA or TA2 terms as their preferred anatomical terms. TA and TA2, like their predecessors ( Nomina Anatomica ), are structured lists of anatomical terms that are familiar and useful to anatomists, physicians, medical researchers, and medical students. A few anatomical websites purport to present Terminologia Anatomica , sometimes with TA’s hierarchy of terms (which could be a copyright infringement), sometimes with unauthorized revisions of TA terms, and sometimes as a searchable database of TA terms, which should be considered, like those in TA2, to be in the public domain. It was an explicit goal of the TA2Viewer collaboration to deliver a high-quality terminology viewer application that avoids diverging development and remains true to the new TA2 standard. TA2 provides an excellent foundation for labeling anatomical structures (even accepting that some structures, such as pathology or specialized anatomy, are not always within the scope of TA2). Once the Open Anatomy Project decided to adopt TA2 for labeling structures in images and reconstructions, the objective of TA2Viewer was broadened to providing users with access to a high-quality anatomical nomenclature using a convenient online tool, and then broadened again to providing information about anatomical terms and structures beyond those strictly available in TA2, such as equivalent terms in other languages, PubMed searches, links to other online biomedical resources, and collections of copyright-free images. In addition to pedagogical use, this extra information provides the user with greater confidence in labeling; for instance, when choosing between two closely related terms. By using TA2 as a common reference nomenclature for anatomy, TA2Viewer serves as a convenient and dynamic index for the fragmented world of biomedical terminology. 

DATABASE To implement the TA2Viewer knowledge base, the TA2 nomenclature was imported from the original FIPAT-published documents and stored in an internal database that included both term entries and term notes. This database is updated whenever errata for TA2 are published, thereby remaining consistent with the standard. It is compiled into an efficient compressed form for use in the TA2Viewer application. As a matter of policy, TA2Viewer represents the published TA2 exactly (with one exception noted below). Any discrepancy between TA2 and TA2Viewer is considered a bug. This policy precludes any situation in which the TA2Viewer version of TA2 diverges from the actual published standard, eliminating confusion or conflict about which version is normative. The single deviation between TA2 and TA2Viewer involves the initial capitalization of terms. TA2, and TA before it, traditionally capitalizes the initial letter of the term. In the printed representation of the standard designed for human interpretation, this capitalization is appropriate. However, more generally, anatomical terms can be used in textual contexts where initial capitalization is incorrect (such as a reference to “arm” or “heart” in running text). Moreover, there are cases where words in a TA2 term of the nomenclature are capitalized (such as the circle of Willis/circulus Willisi, a related term for the cerebral arterial circle). It is important to recognize the significance of these capitalized words as distinct from leading initial capitalization. TA2Viewer stores terms without initial capitalization but capitalizes them when they are displayed. 

SOFTWARE IMPLEMENTATION The TA2Viewer user interface is implemented as a web-based single-page application designed for use with multiple modern web browsers running on desktop and laptop computers, tablets, and mobile phones (although mobile functionality is limited and not fully tested). TAViewer is written in JavaScript using the React framework ( https://react.dev/ ) and the Ant Design user interface toolkit ( https://ant.design/ ). The application is deployed using the Netlify content distribution system ( https://www.netlify.com/ ), which provides high-speed worldwide network access. 

USER INTERFACE The TAViewer application consists of three main components: a toolbar, a hierarchy panel, and a main panel . These components are described in the following sections. 5.1 | Toolbar 5.1.1 | Toolbar elements The toolbar, located at the top of the interface, contains the following elements: Title and home button: The application name, which when clicked returns to the front page of TA2Viewer. Search box: The Search box, placed at the top of the interface, allows users to find structures using the first few letters of the words in any structure’s name, synonym, or related term. Search can also optionally use nonnormative translations extracted from Wikidata to provide multilingual searches in hundreds of languages . The interactive search is described in detail below. Terminology language selector: The language selection pop-up menu sets the primary language used for the nomenclature. The change in nomenclature language occurs instantly in the TA2Viewer interface. A language choice between Latin and English—with both American (US) and British (UK) dialects—is currently available. Other languages will be added as official translations of TA2 are provided by IFAA member societies. Settings button: The settings button pops up a window that allows the user to select an interface language to replace the default English and to widen the capability of the search tool. Currently, there are 15 other options for the interface language: Arabic, German, Spanish, French, Hindi, Indonesian, Italian, Japanese, Nepali, Norwegian, Portuguese, Russian, Swedish, Turkish, and Mandarin Chinese. Users can also choose to include the translations of anatomical terms found in Wikidata (see below) in the searches from the toolbar. Help button: The “?” (help) button currently returns the user to the home page for information about TA2 and TA2Viewer. Additional help material will be added in future releases. 5.1.2 | Language support: Internationalization and translation TA2Viewer uses three different types of language support. First, all TA2 entries have official Latin terms, and US and UK English equivalents, with provisions for the future inclusion of officially ratified equivalents in other languages from IFAA member societies. Second, the search can use unofficial Wikidata translations of terms to access corresponding terms. Finally, the TA2Viewer user interface is translated into 15 different languages, primarily using automatic translation techniques. In future, we hope to streamline the process of translating the user interface to encourage more translations and to permit more users to access the application in their native language. 5.1.3 | Interactive search TA2Viewer’s search functionality is designed to empower a wide range of users to locate terms quickly no matter where those terms are located in the term hierarchy. The application’s internal search engine indexes the official TA2 Latin, UK and US English, associated official synonyms, related terms, the TA2 ID itself, and optionally other related terms from external sources (as described below). TA2’s internal search engine uses a data structure specifically designed for its interactive prefix search. The user need only type the first few letters of any of a term’s names, synonyms, or translations to see matching items in a drop-down list . If a term name consists of multiple words, the prefix must match at least one of those words. The user can include multiple prefixes in the search box; in this case, at least one word in a term name must match each prefix. Order is not important. The search input “sys car,” for example, will map to “cardiovascular system,” while “ner sys” will match “nervous system,” “central nervous system,” “peripheral nervous system,” and matches for four other terms. Prefix search works for any language, not just ones based on the Latin character set. If Wikidata search is enabled in the Settings panel, search is even handled correctly for languages with right to left scripts such as Arabic. The search algorithm uses simple heuristics to improve the ranking of the different matches. Matches in the target TA2 language are prioritized, as are exact matches. Shorter strings are also prioritized. In other cases, if the search string matches a term name in a language that is different from the current preferred language, that matching term name is shown, followed by the term name in the preferred language in brackets. In addition, search using Wikidata’s synonyms for TA2 terms can be enabled using the application settings . When Wikidata synonyms are enabled for search, TA2Viewer uses the appropriate character set to display term synonyms correctly in a wide range of languages. It correctly handles complexities such as right-to-left writing systems, e.g., Arabic . In some cases, a term name maps to multiple TA2 terms with different TA2 IDs. In TA2, there are cross-references among these terms that define “primary” and “secondary” usage of them. To help the user disambiguate these terms while searching, the interface provides the name of an ancestor structure, typically an organ system that disambiguates the usage. For example, the term “abdominal cavity” is listed as both TA2 term 3700, which is part of the abdominopelvic cavity and represents the primary usage, and 128, which is part of the abdomen and represents the secondary usage . Interactive searching and updating of the web user interface can be computationally intensive when a large number of terms match a particular search input, particularly on less powerful devices. To prevent the search computation from interfering with interactive performance, the maximum number of terms displayed is currently set to 500 entries. 5.2 | Hierarchy panel This scrollable column, on the left, below the toolbar, displays a selectable portion of TA2’s hierarchy with the name of each visible entry. Initially, the panel shows the six terms of the upper level of the hierarchy . The hierarchical listing can be expanded to reveal a term’s descendants or collapsed to hide a branch. If a term is chosen from a search of the database, the displayed portion of the TA2 hierarchy automatically changes. The currently selected term is highlighted in blue . 5.3 | Main panel The main panel, located to the right of the hierarchy panel, shows a collection of information about a selected anatomical term . The upper half of the main panel displays the information about the term from TA2. The bottom half displays information derived from other online sources and clickable links to external web pages. A horizontal line separates the official TA2 information above from the collection of nonnormative external data sources below. These external data sources are further divided into two subsections: external searches of other sites and services based on TA2 Latin or English terms, and unofficial cross-references that use TA2 IDs or terms to look up specific anatomical records from external websites. The depth of the terminology of TA2 and its intentional and historical alignment with common clinical use makes the nomenclature well suited for searching and cross-referencing. 5.3.1 | Core information from TA2 The upper half of the main panel always has at least five entries. Heading: The name of the entity, in the language specified in the toolbar. Path: Complete lineage from the top level of the TA2 hierarchy down to the term, with clickable elements. Latin term: The official term in TA2. English term: The English equivalent of the official Latin term. If the UK and US English terms differ, they are listed on separate lines. Term number: The serial number of the term within TA2. 5.3.2 | Optional information from TA2 Additional entries can be shown below the obligate ones in the upper half of the main panel. These entries appear if TA2 contains additional information about the entity. Sex: Specified as ♂ or ♀; included if the entity is sex-specific. Inconstant: Marked as “Yes” if the term was enclosed in parentheses in TA2, indicating that the entity is not considered to be consistently present. Latin synonyms: Listed if Latin synonyms are officially recognized in TA2. English synonyms: Listed if English synonyms are officially recognized in TA2. Related terms: Listed if present in TA2. Related terms are terms that have been used as synonyms but are not currently recognized as such by FIPAT. They include obsolete terms, near synonyms and eponyms . Children: If the entity has children in TA2, two numbers are indicated: the number of immediate children of the term and the number of total descendants of the term. The children are revealed as clickable terms by clicking on the arrowhead to the left of the word “Children.” Primary/Secondary usage: Cross-references when terms are duplicated across two different parts of the hierarchy, distinguished by a unique parent term (see ). Notes: Listed if TA2 includes notes about the term, either new or from previous standard nomenclatures. 5.3.3 | External term search In this section of the main panel, links allow users to perform search queries of TA2 terms conveniently on other internet sites without having to enter or cut and paste text into other websites. The US English term is used as the query in PubMed and Radiopaedia searches. Google search queries add the Latin term to broaden the search and the word “anatomy” to reduce the number of false positives. Google web search: for relevant web pages using https://www.google.com . Google image search: for images using https://www.google.com image search. PubMed search: for clinical and research articles using https://www.ncbi.nlm.nih.gov/pubmed . Radiopaedia search: for radiology images using https://radiopaedia.org . 5.3.4 | Unofficial cross-references This last section of the main panel provides links to records in other online data sources, unofficial translations in numerous languages and images . TA2Viewer uses cross-references between TA2 and other sources from Wikidata, which were created by the Wikipedia community, to make this feature possible. This section is a portal to the following resources: FMA: The Foundational Model of Anatomy, a human anatomy ontology . MeSH: Medical Subject Headings, the controlled biomedical vocabulary used by the National Library of Medicine (NLM) to index articles in the Medline/PubMed database . NeuroNames: A mammalian neuroanatomy terminology that has been developed into an ontology . UBERON: A comparative anatomy ontology . UMLS: Unified Medical Language System, a compendium of controlled biomedical vocabularies created by the NLM . Gray’s Anatomy (20th ed.): The out-of-copyright edition has been republished online by Bartleby.com . Wikipedia: The online, open access English language encyclopedia ( en.wikipedia.org ). Wikidata: The online, open access knowledge base ( wikidata.org ). Wikipedia sites: Links to Wikipedia articles in other languages ( wikipedia.org ). Wikidata translations: Equivalent terms in Latin, English, and many other languages (these terms can also be used for interactive search within TA2Viewer if this option is selected in the settings menu). Wikipedia images: The images contained in English language Wikipedia article. Neither the Open Anatomy Project nor FIPAT evaluates the links that Wikidata provides to other information sources. Although this information is neither standardized nor formally curated, it provides a simple way to extend the usability of TA2 terminology to the broadest audience across the globe. Additional references can be added in future as the resources are added to Wikidata or are otherwise linked to TA2 terms. 

Toolbar 5.1.1 | Toolbar elements The toolbar, located at the top of the interface, contains the following elements: Title and home button: The application name, which when clicked returns to the front page of TA2Viewer. Search box: The Search box, placed at the top of the interface, allows users to find structures using the first few letters of the words in any structure’s name, synonym, or related term. Search can also optionally use nonnormative translations extracted from Wikidata to provide multilingual searches in hundreds of languages . The interactive search is described in detail below. Terminology language selector: The language selection pop-up menu sets the primary language used for the nomenclature. The change in nomenclature language occurs instantly in the TA2Viewer interface. A language choice between Latin and English—with both American (US) and British (UK) dialects—is currently available. Other languages will be added as official translations of TA2 are provided by IFAA member societies. Settings button: The settings button pops up a window that allows the user to select an interface language to replace the default English and to widen the capability of the search tool. Currently, there are 15 other options for the interface language: Arabic, German, Spanish, French, Hindi, Indonesian, Italian, Japanese, Nepali, Norwegian, Portuguese, Russian, Swedish, Turkish, and Mandarin Chinese. Users can also choose to include the translations of anatomical terms found in Wikidata (see below) in the searches from the toolbar. Help button: The “?” (help) button currently returns the user to the home page for information about TA2 and TA2Viewer. Additional help material will be added in future releases. 5.1.2 | Language support: Internationalization and translation TA2Viewer uses three different types of language support. First, all TA2 entries have official Latin terms, and US and UK English equivalents, with provisions for the future inclusion of officially ratified equivalents in other languages from IFAA member societies. Second, the search can use unofficial Wikidata translations of terms to access corresponding terms. Finally, the TA2Viewer user interface is translated into 15 different languages, primarily using automatic translation techniques. In future, we hope to streamline the process of translating the user interface to encourage more translations and to permit more users to access the application in their native language. 5.1.3 | Interactive search TA2Viewer’s search functionality is designed to empower a wide range of users to locate terms quickly no matter where those terms are located in the term hierarchy. The application’s internal search engine indexes the official TA2 Latin, UK and US English, associated official synonyms, related terms, the TA2 ID itself, and optionally other related terms from external sources (as described below). TA2’s internal search engine uses a data structure specifically designed for its interactive prefix search. The user need only type the first few letters of any of a term’s names, synonyms, or translations to see matching items in a drop-down list . If a term name consists of multiple words, the prefix must match at least one of those words. The user can include multiple prefixes in the search box; in this case, at least one word in a term name must match each prefix. Order is not important. The search input “sys car,” for example, will map to “cardiovascular system,” while “ner sys” will match “nervous system,” “central nervous system,” “peripheral nervous system,” and matches for four other terms. Prefix search works for any language, not just ones based on the Latin character set. If Wikidata search is enabled in the Settings panel, search is even handled correctly for languages with right to left scripts such as Arabic. The search algorithm uses simple heuristics to improve the ranking of the different matches. Matches in the target TA2 language are prioritized, as are exact matches. Shorter strings are also prioritized. In other cases, if the search string matches a term name in a language that is different from the current preferred language, that matching term name is shown, followed by the term name in the preferred language in brackets. In addition, search using Wikidata’s synonyms for TA2 terms can be enabled using the application settings . When Wikidata synonyms are enabled for search, TA2Viewer uses the appropriate character set to display term synonyms correctly in a wide range of languages. It correctly handles complexities such as right-to-left writing systems, e.g., Arabic . In some cases, a term name maps to multiple TA2 terms with different TA2 IDs. In TA2, there are cross-references among these terms that define “primary” and “secondary” usage of them. To help the user disambiguate these terms while searching, the interface provides the name of an ancestor structure, typically an organ system that disambiguates the usage. For example, the term “abdominal cavity” is listed as both TA2 term 3700, which is part of the abdominopelvic cavity and represents the primary usage, and 128, which is part of the abdomen and represents the secondary usage . Interactive searching and updating of the web user interface can be computationally intensive when a large number of terms match a particular search input, particularly on less powerful devices. To prevent the search computation from interfering with interactive performance, the maximum number of terms displayed is currently set to 500 entries. 

Toolbar elements The toolbar, located at the top of the interface, contains the following elements: Title and home button: The application name, which when clicked returns to the front page of TA2Viewer. Search box: The Search box, placed at the top of the interface, allows users to find structures using the first few letters of the words in any structure’s name, synonym, or related term. Search can also optionally use nonnormative translations extracted from Wikidata to provide multilingual searches in hundreds of languages . The interactive search is described in detail below. Terminology language selector: The language selection pop-up menu sets the primary language used for the nomenclature. The change in nomenclature language occurs instantly in the TA2Viewer interface. A language choice between Latin and English—with both American (US) and British (UK) dialects—is currently available. Other languages will be added as official translations of TA2 are provided by IFAA member societies. Settings button: The settings button pops up a window that allows the user to select an interface language to replace the default English and to widen the capability of the search tool. Currently, there are 15 other options for the interface language: Arabic, German, Spanish, French, Hindi, Indonesian, Italian, Japanese, Nepali, Norwegian, Portuguese, Russian, Swedish, Turkish, and Mandarin Chinese. Users can also choose to include the translations of anatomical terms found in Wikidata (see below) in the searches from the toolbar. Help button: The “?” (help) button currently returns the user to the home page for information about TA2 and TA2Viewer. Additional help material will be added in future releases. 

Language support: Internationalization and translation TA2Viewer uses three different types of language support. First, all TA2 entries have official Latin terms, and US and UK English equivalents, with provisions for the future inclusion of officially ratified equivalents in other languages from IFAA member societies. Second, the search can use unofficial Wikidata translations of terms to access corresponding terms. Finally, the TA2Viewer user interface is translated into 15 different languages, primarily using automatic translation techniques. In future, we hope to streamline the process of translating the user interface to encourage more translations and to permit more users to access the application in their native language. 

Interactive search TA2Viewer’s search functionality is designed to empower a wide range of users to locate terms quickly no matter where those terms are located in the term hierarchy. The application’s internal search engine indexes the official TA2 Latin, UK and US English, associated official synonyms, related terms, the TA2 ID itself, and optionally other related terms from external sources (as described below). TA2’s internal search engine uses a data structure specifically designed for its interactive prefix search. The user need only type the first few letters of any of a term’s names, synonyms, or translations to see matching items in a drop-down list . If a term name consists of multiple words, the prefix must match at least one of those words. The user can include multiple prefixes in the search box; in this case, at least one word in a term name must match each prefix. Order is not important. The search input “sys car,” for example, will map to “cardiovascular system,” while “ner sys” will match “nervous system,” “central nervous system,” “peripheral nervous system,” and matches for four other terms. Prefix search works for any language, not just ones based on the Latin character set. If Wikidata search is enabled in the Settings panel, search is even handled correctly for languages with right to left scripts such as Arabic. The search algorithm uses simple heuristics to improve the ranking of the different matches. Matches in the target TA2 language are prioritized, as are exact matches. Shorter strings are also prioritized. In other cases, if the search string matches a term name in a language that is different from the current preferred language, that matching term name is shown, followed by the term name in the preferred language in brackets. In addition, search using Wikidata’s synonyms for TA2 terms can be enabled using the application settings . When Wikidata synonyms are enabled for search, TA2Viewer uses the appropriate character set to display term synonyms correctly in a wide range of languages. It correctly handles complexities such as right-to-left writing systems, e.g., Arabic . In some cases, a term name maps to multiple TA2 terms with different TA2 IDs. In TA2, there are cross-references among these terms that define “primary” and “secondary” usage of them. To help the user disambiguate these terms while searching, the interface provides the name of an ancestor structure, typically an organ system that disambiguates the usage. For example, the term “abdominal cavity” is listed as both TA2 term 3700, which is part of the abdominopelvic cavity and represents the primary usage, and 128, which is part of the abdomen and represents the secondary usage . Interactive searching and updating of the web user interface can be computationally intensive when a large number of terms match a particular search input, particularly on less powerful devices. To prevent the search computation from interfering with interactive performance, the maximum number of terms displayed is currently set to 500 entries. 

Hierarchy panel This scrollable column, on the left, below the toolbar, displays a selectable portion of TA2’s hierarchy with the name of each visible entry. Initially, the panel shows the six terms of the upper level of the hierarchy . The hierarchical listing can be expanded to reveal a term’s descendants or collapsed to hide a branch. If a term is chosen from a search of the database, the displayed portion of the TA2 hierarchy automatically changes. The currently selected term is highlighted in blue . 

Main panel The main panel, located to the right of the hierarchy panel, shows a collection of information about a selected anatomical term . The upper half of the main panel displays the information about the term from TA2. The bottom half displays information derived from other online sources and clickable links to external web pages. A horizontal line separates the official TA2 information above from the collection of nonnormative external data sources below. These external data sources are further divided into two subsections: external searches of other sites and services based on TA2 Latin or English terms, and unofficial cross-references that use TA2 IDs or terms to look up specific anatomical records from external websites. The depth of the terminology of TA2 and its intentional and historical alignment with common clinical use makes the nomenclature well suited for searching and cross-referencing. 5.3.1 | Core information from TA2 The upper half of the main panel always has at least five entries. Heading: The name of the entity, in the language specified in the toolbar. Path: Complete lineage from the top level of the TA2 hierarchy down to the term, with clickable elements. Latin term: The official term in TA2. English term: The English equivalent of the official Latin term. If the UK and US English terms differ, they are listed on separate lines. Term number: The serial number of the term within TA2. 5.3.2 | Optional information from TA2 Additional entries can be shown below the obligate ones in the upper half of the main panel. These entries appear if TA2 contains additional information about the entity. Sex: Specified as ♂ or ♀; included if the entity is sex-specific. Inconstant: Marked as “Yes” if the term was enclosed in parentheses in TA2, indicating that the entity is not considered to be consistently present. Latin synonyms: Listed if Latin synonyms are officially recognized in TA2. English synonyms: Listed if English synonyms are officially recognized in TA2. Related terms: Listed if present in TA2. Related terms are terms that have been used as synonyms but are not currently recognized as such by FIPAT. They include obsolete terms, near synonyms and eponyms . Children: If the entity has children in TA2, two numbers are indicated: the number of immediate children of the term and the number of total descendants of the term. The children are revealed as clickable terms by clicking on the arrowhead to the left of the word “Children.” Primary/Secondary usage: Cross-references when terms are duplicated across two different parts of the hierarchy, distinguished by a unique parent term (see ). Notes: Listed if TA2 includes notes about the term, either new or from previous standard nomenclatures. 5.3.3 | External term search In this section of the main panel, links allow users to perform search queries of TA2 terms conveniently on other internet sites without having to enter or cut and paste text into other websites. The US English term is used as the query in PubMed and Radiopaedia searches. Google search queries add the Latin term to broaden the search and the word “anatomy” to reduce the number of false positives. Google web search: for relevant web pages using https://www.google.com . Google image search: for images using https://www.google.com image search. PubMed search: for clinical and research articles using https://www.ncbi.nlm.nih.gov/pubmed . Radiopaedia search: for radiology images using https://radiopaedia.org . 5.3.4 | Unofficial cross-references This last section of the main panel provides links to records in other online data sources, unofficial translations in numerous languages and images . TA2Viewer uses cross-references between TA2 and other sources from Wikidata, which were created by the Wikipedia community, to make this feature possible. This section is a portal to the following resources: FMA: The Foundational Model of Anatomy, a human anatomy ontology . MeSH: Medical Subject Headings, the controlled biomedical vocabulary used by the National Library of Medicine (NLM) to index articles in the Medline/PubMed database . NeuroNames: A mammalian neuroanatomy terminology that has been developed into an ontology . UBERON: A comparative anatomy ontology . UMLS: Unified Medical Language System, a compendium of controlled biomedical vocabularies created by the NLM . Gray’s Anatomy (20th ed.): The out-of-copyright edition has been republished online by Bartleby.com . Wikipedia: The online, open access English language encyclopedia ( en.wikipedia.org ). Wikidata: The online, open access knowledge base ( wikidata.org ). Wikipedia sites: Links to Wikipedia articles in other languages ( wikipedia.org ). Wikidata translations: Equivalent terms in Latin, English, and many other languages (these terms can also be used for interactive search within TA2Viewer if this option is selected in the settings menu). Wikipedia images: The images contained in English language Wikipedia article. Neither the Open Anatomy Project nor FIPAT evaluates the links that Wikidata provides to other information sources. Although this information is neither standardized nor formally curated, it provides a simple way to extend the usability of TA2 terminology to the broadest audience across the globe. Additional references can be added in future as the resources are added to Wikidata or are otherwise linked to TA2 terms. 

Core information from TA2 The upper half of the main panel always has at least five entries. Heading: The name of the entity, in the language specified in the toolbar. Path: Complete lineage from the top level of the TA2 hierarchy down to the term, with clickable elements. Latin term: The official term in TA2. English term: The English equivalent of the official Latin term. If the UK and US English terms differ, they are listed on separate lines. Term number: The serial number of the term within TA2. 

Optional information from TA2 Additional entries can be shown below the obligate ones in the upper half of the main panel. These entries appear if TA2 contains additional information about the entity. Sex: Specified as ♂ or ♀; included if the entity is sex-specific. Inconstant: Marked as “Yes” if the term was enclosed in parentheses in TA2, indicating that the entity is not considered to be consistently present. Latin synonyms: Listed if Latin synonyms are officially recognized in TA2. English synonyms: Listed if English synonyms are officially recognized in TA2. Related terms: Listed if present in TA2. Related terms are terms that have been used as synonyms but are not currently recognized as such by FIPAT. They include obsolete terms, near synonyms and eponyms . Children: If the entity has children in TA2, two numbers are indicated: the number of immediate children of the term and the number of total descendants of the term. The children are revealed as clickable terms by clicking on the arrowhead to the left of the word “Children.” Primary/Secondary usage: Cross-references when terms are duplicated across two different parts of the hierarchy, distinguished by a unique parent term (see ). Notes: Listed if TA2 includes notes about the term, either new or from previous standard nomenclatures. 

External term search In this section of the main panel, links allow users to perform search queries of TA2 terms conveniently on other internet sites without having to enter or cut and paste text into other websites. The US English term is used as the query in PubMed and Radiopaedia searches. Google search queries add the Latin term to broaden the search and the word “anatomy” to reduce the number of false positives. Google web search: for relevant web pages using https://www.google.com . Google image search: for images using https://www.google.com image search. PubMed search: for clinical and research articles using https://www.ncbi.nlm.nih.gov/pubmed . Radiopaedia search: for radiology images using https://radiopaedia.org . 

Unofficial cross-references This last section of the main panel provides links to records in other online data sources, unofficial translations in numerous languages and images . TA2Viewer uses cross-references between TA2 and other sources from Wikidata, which were created by the Wikipedia community, to make this feature possible. This section is a portal to the following resources: FMA: The Foundational Model of Anatomy, a human anatomy ontology . MeSH: Medical Subject Headings, the controlled biomedical vocabulary used by the National Library of Medicine (NLM) to index articles in the Medline/PubMed database . NeuroNames: A mammalian neuroanatomy terminology that has been developed into an ontology . UBERON: A comparative anatomy ontology . UMLS: Unified Medical Language System, a compendium of controlled biomedical vocabularies created by the NLM . Gray’s Anatomy (20th ed.): The out-of-copyright edition has been republished online by Bartleby.com . Wikipedia: The online, open access English language encyclopedia ( en.wikipedia.org ). Wikidata: The online, open access knowledge base ( wikidata.org ). Wikipedia sites: Links to Wikipedia articles in other languages ( wikipedia.org ). Wikidata translations: Equivalent terms in Latin, English, and many other languages (these terms can also be used for interactive search within TA2Viewer if this option is selected in the settings menu). Wikipedia images: The images contained in English language Wikipedia article. Neither the Open Anatomy Project nor FIPAT evaluates the links that Wikidata provides to other information sources. Although this information is neither standardized nor formally curated, it provides a simple way to extend the usability of TA2 terminology to the broadest audience across the globe. Additional references can be added in future as the resources are added to Wikidata or are otherwise linked to TA2 terms. 

DISCUSSION TA2Viewer addresses shortcomings in existing online anatomy term browsers while providing features not found in other online resources. It allows interactive browsing of TA2 in Latin, US English, and UK English, with the capacity for adding further official translations when they are provided by member anatomical societies. Through collaboration between IFAA and the Open Anatomy Project, TA2Viewer is a faithful and accurate representation of TA2. The “any content discrepancy from TA2 is a bug” development philosophy establishes clear lines of responsibility between nomenclature and software development. Tying the development of TA2Viewer to the authoritative release of TA2 and of errata corrections has proven to have been a wise technical decision. Beyond providing convenient access to TA2, TA2Viewer uses the comprehensiveness and consistency of TA2 as a framework for convenient search of online anatomical information. TA2 terms are used either as a direct index into data sources such as Wikidata, or as search terms into other web indexes such as Google web or image search. As TA2Viewer grows to include more resources, we expect that additional providers of anatomical content will be interested in integrating their content into it. We are actively investigating mechanisms to simplify this process. Including references to externally curated and uncurated resources in TA2Viewer beyond the control of FIPAT naturally entails the possibility that inaccurate anatomical information is disseminated. TA2Viewer was designed with those concerns in mind. Third party information is clearly delineated as external search or unofficial cross-references. Clicking any of the links in these sections is conceptually no different from copying the TA2 term number or text into another web page (except that in some cases, such as Wikipedia image viewing, TA2Viewer provides a nicer interface). Users are generally aware that internet searches sometimes produce inaccurate results. TA2Viewer merely simplifies access to search engines and other resources while clearly separating those results from the TA2 nomenclature itself. In summary, TA2Viewer has exceeded our original project goals for providing the users of the Open Anatomy Project with convenient access to a high-quality anatomical nomenclature. It addresses a need to disseminate accurate medical terminology widely and freely to users worldwide. Using the widely-accepted TA2 nomenclature as an index into the growing wealth of online anatomical information provides value beyond what any single organization or publication is capable of delivering. Finally, TA2Viewer’s powerful ability to provide anatomical term searches across hundreds of languages honors the needs of medical professionals, educators, and students across the globe. We look forward to continuing its development to address the needs of the worldwide biomedical community further. 

