586. There are only three neuters in common use, #cornū#, _horn_,
#genū#, _knee_, and #verū#, _a spit_. But some cases of other neuters
are used: as, ablative #pecū#, _flock_; plural nominative and accusative
#artua#, _limbs_ (Plaut.); OSSVA, _bones_ (inscr.).
587. The nominative of stems in #-u-# ends, including the stem vowel, in
#-u-s# in gender words, and in lengthened #-ū# of the stem in neuters.
588. Most substantives in #-u-# are masculines in #-tu-# or #-su-#,
often defective in case (235). The following words are feminine: #acus#,
_pin_, _needle_, #domus#, _house_, #manus#, _hand_, #porticus#,
_colonnade_; #tribus#, _tribe_; and the plurals #īdūs#, _ides_, and
#quīnquātrūs#, _feast of Minerva_; rarely #penus#, _store_, and
#specus#, _cave_.