The fourth declension.

The Fourth Declension. The words sound like the title of a mystery novel. To many, the fourth deciension is indeed a mystery. It comprises a group of Latin nouns ending in us on u, many of which have survived in modern English. Those ending in us are noteworthy, because their plural and singuIan forms are the same (except that in Latin the us suffix is pronounced in the singular with a short u, like the u in pussycat, and in the plural with a long U, like the oo in moose). There are words in English, such as sheep, that are the same in the singular and plural, but in scientific English we are not comfortable with being unable to differentiate numben. Attempts to avoid the problem have caused some confusion in nomenclature. E. Frederick Lang (personal communication) was disappointed that I failed to discuss nouns like meatus, sinus, hiatus, and habitus in a previous vignette on plurals [1], and Konnad Kirchen (personal communication) has pointed out that I muddied the waters concerning adnexus [2]. Meatus (Latin: a passage on channel) is used in medical nomenclature for the opening of a canal. Most physicians would (incorrectly) give meati as the plural of meatus. Because it is a fourth-declension Latin noun, its plural is meatLis. Those who know the correct Latin plural usually feel awkward saying meatUs and substitute the anglicized form meatuses. Sinus is another fourth-declension noun (Latin: cavity or hollow). Its plural is sinJs, but I do not recall even seeing that plural form in English. The anglicized sinuses is the accepted form, again to avoid the confusing fourth-declension plural. Similarly, hiatus (Latin: aperture), habitus (Latin: form, condition, demeanor, manner, bearing), and fetus (Latin: offspring) are fourth-declension nouns with plurals hiatUs, habiff15, and fetUs. Most of us use the anglicized versions hiatuses, habituses, and fetuses, although a few erroneously construct an iending. Perhaps the most confusing fourth-declension noun in medical nomenclature is adnexus. Here I have an opportunity to clarify my previous remarks [2]. Standard English dictionanies [3] cite: Adnexa, neuter plural of Latin adnexus = (Anat.) accessory pants or appendages of an organ. Reference to a Latin dictionary [4], however, yields adnexus, us (fourth declension) masculine noun = a fastening, attaching, connexion. How can adnexa be neuter plural c’f a masculine noun? Adnexus is fourth deciension, so its plural should be adnexus, not adnexa. For some reason, the usual English solution to the fourth-declension plural problem (adding es to the singular to make the plural) was not used in the case of adnexus. instead, a completely different approach was used. The Latin verb adnectere means to tie, bind, or attach to. The past participle is adnectus or adnexus on annexus. (From annexus comes the English word annex.) In other words, adnexus can be not only a masculine fourth-declension noun but also the masculine adjectival form of the past participle of adnectene. (Past participles can be used as adjectives in both Latin and English-hence “the attached thing. “) The neuter plural adjectival form of the past panticipie of the verb adnectere is adnexa. This led to the anomabus situation in which the masculine singular noun adnexus was used for a singular appendage, whereas the neuter plunal adjectival form of the past participle of the verb adnectere (adnexa) was used instead of the masculine plural noun adnexUs to signify plural appendages. I note that Stedman’s Medical Dictionary [5] now uses adnexum (neuter singular past participle) for the singular form to “rationalize” this anomaly. However, this approach is not etymologically ideal. Substituting a neuter adjectival form of the past participle of a verb for a masculine noun in order to avoid an awkward plural is the linguistic equivalent of walking around the block so as not to step on a crack in the sidewalk, an unnecessanily complicated solution to a simple problem. For better or for worse, however, we are stuck with it. Not all nouns of Latin origin ending in us are fourthdeclension nouns spelled the same in singular and plural. For example: sulcus (Latin: furrow, ditch), nucleus (Latin: littie nut, kennel), and radius (Latin: spoke of a wheel) are second-declension nouns that take i in the plural; hence sulci, nuclei, radii. English is not the only language with infuniatingly arbitrary rules of grammar.