399. The stem contains the meaning of the noun. Noun stems are arranged
in the following order: (1.) stems in #-ā-#, in #-o-#, in a consonant,
or in #-i-#; these are substantive, including proper names, or
adjective; (2.) stems in #-u-# or #-ē-#; these are substantive only, and
include no proper names.
400. In some instances, a final stem vowel is retained before a case
ending which begins with a vowel: as, #urbi-um#, #ācri-a#, #cornu-a#,
#portu-ī#, #portu-um# (116, _c_); in others the stem vowel blends
inseparably with the vowel of the case ending: as, #mēnsīs#, #dominīs#
(108, _a_).